I doubt that this solves it. The early game pios would be fine because they already got the veterancy. Late game pios still have no chance. Conscripts had similar problems before their buff: A vet3 Conscript from the early game was alright, but if you lost them they had no chance of vetting up again and just got shredded
But replacing lost mainlines is completely different from replacing engineers. If you're issue is that you lost your pioneers and the new ones you built aren't holding up in combat, I mean, that's tough. They aren't supposed to, and my received accuracy suggestion is only meant to help them a little
Biggest reason to want vetted engineers is the repair bonus at vet 2, and they already added a repair speed bonus to the sweeper
Best solution would still be if mine sweeping would give XP. That way especially sweeper squads would be able to vet up. Or just give a small amount of shared veterancy for pioneer units with a sweeper.
I have said this for years, they should also get XP from kills/damage they do with planted mines. It seems the modteam doesn't want this or its not possible because its never made it to a patch