Outside of that heavy sapper upgrade gives sapper Enfeilds in place of sten.
I do feel like Anvil is kind of less attractive now that Comet isn't absolute Trash. Heavy Sappers have always been kind of weird since the Vickers has complete opposite damage curve of Stens. I think if you gave them a Suppression ability that would fit the defensive theme of Anvil OR if Heavy Sappers gained an Emplacement Garrison Bonus +1 so that if you park them inside an emplacement then it's a bigger bonus than usual.
Edit - Also please fix "Hold the Line" in Special Weapons or replace it with another ability.
Also Pak Howie damage nerf kthxbye.