Rifles cost 280mp.
Reinforce for 4x28=112mp.
112 is 40% of 280.
Grens cost 240mp.
Reinforce for 3x30=90mp.
90 is 37,5% of 240.
Universal reinforce formula aims to give unit reinforce cost to full for 40% of total worth(less for weapon teams as not all members are combat potent), so following that, grens are slightly underpriced when reinforcing, but that balances out by them having 7 pop instead of 6 for other 240mp units.
when looking at it that way its true..
but i try to look at it this way: when you are buying a new rifleman squad you pay 56 mp per model and when buying a new gren squad you pay 60 mp per model. and when comparing the fire power you get for your manpower you are getting a much better deal when buying rifleman.