and all you have said about them uptill then was EHP
i suggest you actually use them in live game to get a grip of what they are now, then may be provide some replay of your "tests"? a couple of k dmg again AI or some win on empty test map mean very little.
I live the are build in T1 and heavy sapper have moving penalty both changes are a huge buff to them.
a ton of munition for a mediocer performance and locking out the comet isnt "drawbacks", sure, im done with this.
The upgrade at 60 mu for repair speed, weapons and armor is one of the cheapest upgrade in game.
Comet/Churchill are separate issues.
In the preview there are no real drawback in getting the upgrade and still remain a badly desing upgrade.
there are nothing wrong with the fact that an unit can punch above there weight with that kind of invesment, i pay triple the amount of munition to get similar lever of performance.
The unit perform above it cost and role with heavy Sapper upgrade alone, it does need any other weapons upgrades, that 3 weapons option is simply the icing on the cake.
If you compare them with engineers from other faction it is evident.