Lower ranks are there on purpose as the tradeoffs aren't worth. I aimed for 30% strength for 90% damage reduction on 2, as close to 75% at 70% efficiency for easy spam and refresh on 2, nice range at 225% (can go lower, test yourself I still am, can add more health), bit of duration as I don't see the point your number 2 just gets refreshed and the [Extend] on your 4 is enough as is and the drain is not too much if you even expand it.

For budget use [Constitution] instead of [Augur Message] and normal [Continuity], this makes your 2 only 21 seconds but thats plenty of time anyway.

The explosion on your 4 scales off of your 1 damage, which in turn scales with your melee weapon mods so scale the total damage on your melee as high as possible.

Arcanes you can go for as second:
-Arcane Aegis: Some more tankiness
-Arcane Blade Charger: More damage on your shatter for a while after you kill with primary
-Arcane [Fury]: Same as Blade Charger