True and merge also becomes more risky later on when tanks arrive. They can reguraly kill 2 models and in some cases just before you merge and cost you the cons squad. But that limited to in combat. For recrewing its really good when you get 7th man.
4 to 7 mp more per model is imo not gamebreaking. It takes seconds to gain that amount of mp. The mp soviets save with merge and cheaper reinforcing goes into replacing vehicles wich for the most part get destroyed easier/faster then axis tanks. This comes from 1v1 perspective ofcourse.
In my experience in the late game pio's just as ce's are not priorities to focus fire on mostly. Only with flamers or when repairing they are and they both will melt away when you do so.
The fact combat merge isnt used as much later on doesnt detract from its(powerful) utility early game.
In the late game, cost saving merge like we used to see more often with guards when they were 35(?) MP to reinforce is going to be more common. Using 7 man cons to speed up reinforcing and save on costs can net you 9mp saved per squad reinforced plus a faster return to the battle field for repairs and minesweeping.
In this case the difference between reinforcing a pio or CE squad is up to 21mp and rarely do players only field a single pio or CE squad.
Even without using merge, you still have a 12mp difference in reinforce costs on a SINGLE squad, while there being no difference in durability of the models(unlike cons vs grens).
If 4-7mp per model werent a big deal then you might as well standardize all mainline infantry to 25mp reinforcement.
When you hear people talking about how going double sturmpioneers can result in heavy bleed for OKW, just consider that volks "only" cost 5 less to reinforce and have less durable models to boot. And if you dont think peniles bleed you harder than cons late game(and its noticeable) you must not have tried late game with peniles.
As for late game priorities, pios and CE might not be priorities as far as how dangerous they are, but if you want to bleed your opponent then you absolutely target them since neither gain any durability vet. The only difference is that CE can engage more effectively at safer ranges- and cost less to get back on the field.