the RE, sapper(4 men), sov eng, and wehr pio are all 5 pop. Sturmpio are 8 pops.
2 sturmpop still take 1 more pop than 3 of their counterpart. (16 vs 15) The sapper and RE can both go double ATW + minesweeper as well.
To be fair ive never retreated an mg42 because "combat" "engineers" flanked it, it would actually probably take 3 to be any threat at all...
Cant say the same for sturms
Aside from just general repair duty sturma can also heal 3 squads without vet (and faster than pios who require vet 1)
Even after they have lost their ability to assault they retain the ability for opportunity jumps (especially when armed with a sweeper since they can put it away) and guarding flanks. They are more because they are better, not objectively better, but better in all ways (except for sappers obviously but thats because tommies are super squishy out of cover and bleed like a stomach wound...oh wait)