Exactly, which is why the 7th man upgrade doesn’t really change anything until T4 comes up.
Scaling.
Assault Engineers are stronger than Rifleman at the start of the game, but weaker later on. That's a major decision point: get strong infantry now, or get weaker infantry that'll be stronger later?
The new Panzerfusiliers work on similar logic: they're a weaker opening than Volks, but if you make do with them, you'll be rewarded with much better scaling than you'd get from a Volks squad.
Mixing in Conscripts has a lot of perks: they can merge into anything that's not Shocks, they can build cover your Penals can't and they can keep your flamer on the field. However, current Conscripts have awful scaling. You're not going to make the long term investment in a Con squad or two if you're going to get punished for it.
Now though, they might be appealing.
Also remember, the reinforcement cost bonus isn't just for the Conscript squad itself.
It's also for
everything you merge those Conscripts into.
How does 17 MP to reinforce Guards or Penals sound?