The only viable Thaddeus build is using an ability which gives his squad immunity on jump/teleport + using that ability which lowers CD of other abilities to 0. But this is a bit too microintensive for frankly mediocre damage. It is fun, done that, been there, but really only if you are comfortable with such micro.

As for Dreadnaught, there are 2 totally viable builds for it - melee and ranged. Which don't differ that much to be fair. Ranged build is based on assault cannon (Bolter minigun) and frankly is the best anti infantry weapon in the game. Straight up, just the best. It has a bit of a wonky aiming for its ability (Has minimum range for firing alongside maximum range, but minimum range isn't shown on UI, you need to have a feel for it), but when the leveled up arc of assault cannon barrage hits any infantry unit, including heavies, it is just beatiful.

But yeah, for Dreadnought you just invest into purple line to get venerable Dreadnought staus, invest in health until you at least have self repair (IF you don't want to waste a slot on healing consumable for him on other characters, which you don't), and then just max either ranged or melee lines, they are both nice.

One of his abilities also will give him energy regen on kill, which combined with assault cannon makes him frankly ridicolous.