I've noticed some things about Tankbustas that I'm not sure are intended that way:
1) Burrowing squigs and buildings: I've noticed that if I shoot squigs right next to buildings from long range (turret and core for example) and they don't have another target, they will detonate and damage the building with the AoE. But they don't choose the building as a viable target! So if I have the doctrine with burrowing Squigs, I can't damage buildings if no unit is standing right next to it. I would really like to use this doctrine, but one of the things that make TB's useful is the ability to poke at buildings with the squiggs, so this doctrine actually makes the TB's much worse IMHO.
2) Rocket barrage vs squig: Another thing I noticed is that if you use the doctrine with the AoE rocket-barrage, it puts both the squig-ability and the barrage ability on the full cooldown, no matter which one you've used. This again makes this doctrine pretty much useless.
3) Smartcasting: This is one I've noticed on many things like trukks and tankbustas. If you have multiple tankbustas using an ability, smartcasting doesn't work and they all just shoot at once on the same target location. I don't necessarily mind this, since it makes you use micro, but it's kinda weird that it seems to work for certain units/abilities (like most grenades), but not for others.
Love the game so far, keep up the good work! ^^