Ah, if only DE, could buff him т_т
There are weapons like [Laetum], warframes like [Octavia], [Volt], [Nezha], [Saryn], [Wisp] which are generally very good, but even more amazing in their own specific fields. While [Excalibur] is generally not bad, but sometimes useless and never amazing.

If you're new to the game and just want a strong warframe, i don't recommend you to invest your resources in [Excalibur Umbra]. As there are lot of better options to choose from. But if you still want to play him, this build is for you!

I'm a big [Excalibur] fan. I've been using this warframe for the first 200 hours of my gameplay. I've tried a lot of diffrent builds, subsumes, archon mods etc. This is the best build i've made so far. But it's still very noob friendly and engaging. Plus it's very helpful for your team, as you provide amost endless energy for them, a massive damage buff and corrosive+viral stacks on the enemies. As long as you don't get killed you can melt through 300lvl+ enemies with ease.

For new players:

• Cost First of all, this build might seem little bit too expensive for new players, but i'd like to tell you that it isn't. The primed mods can easily be switched for their normal counterparts. The build can be reduced to just 1-2 forma as well if you skip the eksilus slot and use non-primed mods. I'm just giving you the final version of this build, don't worry friends. You can still easily deal with most of the steel path with just 1 forma and non-maxed, non-primed mods.
• Chromatic Blade if you don't have enough standing with the syndicates it's just 10plat on the market. Actually, i'm sure most of the veteran player can just give it to you for free if you're a nice person.
• The expensive part The only real problem with the cost of this build is farming [Grendel] and having a helminth. But, don't worry, they are not as tough as most of the players make them out to be. Farming Grendel was actually very fun for me, unlike something like Sevagoth.
• Farming Nourish For helminth you just need to get 3rd level rep on deimos. For [Grendel] you just need to get vitus and a party (you can actually get him for free if someone who has a locator takes you with them). Those missions are quite hard to complete alone (you can't use mods on those missions, so how strong you are doesn't really matter).

Main features of the build:

• Chromatic Blade is used in this build as well as on the most of the other [Excalibur Umbra] builds. It benifits greatly from a high ability power as it scales with you ability strength! With this build your [Exalted Blade] umbra will have 160%+ status chance. As most of you know it turns all of your physical damage into elemental damage, depending on your warframe's energy colour. I recommend using heat or electricity colour. I'll explain why later.
• Nourish

Why Nourish? Why not something better? Actually! I don't really think there's anything better! Unlike abilities like roar or gloom, it has multiple benifits for Excalibur:

• Energy sustain This ability effectively multiplies energy gains from all sources by 4 (works great with zenurik). That's why we can just go with 45% energy efficiency and still never turn off our exalted blade while spamming dash and radial-howl.
• Viral damage and procs This ability infuses your weapons (including the [Exalted Blade]) with viral damage. So you don't have to build viral on your [Exalted Blade]. I recommend just going for pure heat+corrosive build. With your 160%+ status chance you'll stack both viral and corrosive incredibly fast,
  just this will multiply your damage a lot more than roar would.
• Bonus damage Just plain 240%+ bonus damage as viral which is a bit worse than 100% multiplicative bonus from roar, as it doesn't double dip on status procs. But it's still a lot.
• Viral procs on taking damage to enemies in base 12m radius This buff applies to your teammates and is just a nice bonus. You can use battle discipline to trigger this, but i wouldn't recommend that in this build.

Exalted Blade Build You should really just build it howewer you like. Who am i to tell you what to do, friend?! Anyways, this is My Build if you're curious. It's a bit silly and expensive (6 forma), but it works well with this build.

If you decide to mod for yourself then my tips with modding the blade would be:

1. Go corrosive. It will get you a lot more damage. This is so absurdly strong when you already have free viral.
2. Go heat or electricity damage through mods or [Chromatic Blade] for the DoT. I recommend using heat.
3. You could skip the heat damage mod, like i do, because you can get it from [Chromatic Blade]'s damage conversion. But you'll get less heat procs that way.
4. Use pure damage elemental mods instead of status elementa mods. You have 900-1000% status chance bonus, something like 60% more status wouldn't matter, really, it's not worth losing damage for this.
5. Use reach/[Primed Reach]. The blade waves do not deal nearly as much damage as the blade itself.
6. [Healing Return] is not as silly as it may seem, you should at least try it out. This build provides plenty of status for this mod to be usefull.
7. Crit damage and attack speed are very nice options. I think, attack speed is by far the best option. (I only use one attack speed mod, because of the arcane).
8. No physical damage mods. It's quite obvious friend!

What about survivability?
Yeah this build doesn't help much with survivability, unlike gloom does. But don't forget, that you have three umbra mods whic make you quite tanky already. There shouldn't be much of a problem surviving on base steel path. You have plenty of armor and hp, you are very mobile and you kill most things in seconds.
I suggest using 3 or more blue archon shards for health regeneration.
Don't forget to use your radial-howl and slash dash when needed.
Use healing return on your blade, or try to use shield-gateing mods instead, i don't like it, because that's a poor game design feature, but it works.
If you still have trouble survivng on steel path, well, that's just how it is. Some enemies just one shot you if you don't shield gate. Doesn't really matter if you have your umbra mods maxed and have 1000+ current hp with lots of armor it's not really possible to tank higher lvl enemies without wrames like [Citrine], [Revenant], [Nezha] and the like. It's really a pity, because his fighing style makes it hard to avoid damage.
Options
Feel free to swap [Continuity] and [Cunning Drift] for something else.
You can use any aura, actually. You have enough damage as is. But, i think Steel Charge is the best damage option. [Corrosive Projection] is not good on this build, because corrosive+heat already strip most of the armor from the enemies.
Molt Augmentet is very optional. I just use it, because most of the people have it maxed anyways.
You can swap [Blind Rage] for something else if you don't have [Primed Flow] yet. Or you can just use blue shards for additional energy storage. And you should really use zenurik with this build.

Tips
You can use [Exalted Blade] on weapon restricted missions. Very useful when you don't have a lot of good weapons.
I reccomend you turn on melee atacks on a fire button in you settings. Mashing that 'E' button get's pretty tiring in a couple of hours.
You can actually just equip trash weapons for ranking them up in normal missions, it's quite slow, but you really don't need to use anything besides your exalted weapon.

So, yeah, i think that's it, mostly. I don't think it's the best possible build, but i'm sure it's close. Does this build make [Excalibur] really strong? Yes it does! Does this buld make [Excalibur] stronger then any other warframe? Not even close, it's still a status build and it's still [Excalibur], so it's quite bad against eidolons, archons and some bosses. Who cares?
I'd still say that [Excalibur] is kind of weak. He's mostly useleess outside of the normal starchart and steelpath, he has terrible aoe, he's not optimal to build him with anything but status, he has to put a lot of effort to survive and to be played efficiently, he doesn't contribute anything to the team and at the same time he's not really the best solo warframe.
If you want the most optimal warframe with the most optimal playstyle just go and do that, don't bother people that are having fun with the game.