Wfa engineers were designed to do a lot of fighting. They are explicitly designed to do less engineering as well. They are meant to be on the front which is why they are better to attain vet and have combat related vet as well.
Not Really WFA engineer are potent "engineer" units the only thing the miss over EFA enginner are the flamers.
EFA engineer design is fairly black and white. They help in the early stages to fight and grab ground, they fall back and build bases once lines are secure, they prepare defenses and caches and then repair armour. They are not supposed to be in the front. Making it so pios can become budget defenders who can already make their own cover, but then see the enemy coming and get into cover and properly defend it will change they dynamic of ost play.
EFA engineers are meant to always be vulnerable and frankly shit in combat. This is very clearly represented in their stats and vet.
Shared vet is a route, vet from mines if possible is a route but changing their weapons to completely eliminate their weakness when they fall off while doing nothing about their strength in their element is bad business. They are not RE and they are not sturms. They are not supposed to be on the front without great risk.
You are simply extenuating the effects of giving bolt action rifle once upgrade with flamer or sweepers would have.
Currently MP-40 do not work either with flamer since the DPS at range +20 plus minimal nor with sweepers with 3 MP40. Allowing to do a little damage at distance will not suddenly make them "front line infatry"