They actually better than grens,volks with vet(if no weapon upgrades involved,even without weapons they do something and if somehow they get lmg they become best squad on map.
Problem is exactly beginning of the game when they at their worst.Lowering mp cost is really bad idea if some ppl can remember cpt.price streams with 20 squads of royal engineers with around 13 mp reinforce
Conscripts late game a certainly not better than grens or volks, because as all of them are getting more durable grens and volks are ALSO doing more damage to offset that. Additionally if I recall properly (and I may be misremebering) cons get a nerfed lmg when they pick one up, so the impact is greatly lessened over the way it used to be.
At any rate saying without weapon upgrades isn't a good metric because both volks and grens WILL have weapon upgrades, it's creating a scenario that cons would win that won't happen in game.
As for the RE thing:
Firstly Cons cost 20mp per man and don't get that cut at any point. Even if they dropper 1mp per tech building which would be the most one might suggest they would still cost 16 per man, which is more than their weapon crews even.
Secondly RE have access to weapon racks making them punch WELL above their price point at launch and managing to cover AT as well. The flexibility AND lack of bleed is what made the sappers so strong.