I mean... It's a 210mp unit that gets increased armour and repair speed.... What more do you want out of it? Should it be fighting off obers? Or mainline infantry with a similar amount of munitions invested? The heavy snapper isn't meant to make sappers a Tommy replacement, it's meant to allow them to contribute if they must. If you are complaining about the combat performance you are using it wrong.
Basicly look at it like this: without the upgrade your sappers are NOT going to be fighting at all. They are going to be repairing. With the upgrade they repair faster AND can sit on the fringes of fights and generate extra value in the time they saved repairing. They are not suddenly shock troops, but they are available to HELP (not carry)
Thas wrong without the upgrade iam able to snare vehicles and engage cc against units like grenadiers or osttruppen.
With the upgrade i cant snare since they are to slow and i have to stay back and even then they can't defend themselves against a chasing squad or a long range lmg unit.
And even their repair speed isn't impressively good, since every other pioneer squad get boosted repair speed with mine sweeper.
I would give them just the armor and the repair speed bonus for less munition without the movement penalty