Assault grens aren't really even worth 320 mp. They are worth 280 but their 0cp call-in threw balance off so badly that they needed to have a prohiitive cost. It was either more manpower or an additional muni cost and the players hated spending more muni. It's why their reinforce cost is still the same as when they were 280.
It was also pre T1/T2 build time buff for soviets and since the buff time I'm constantly repeating that AGs could go back to their 280mp cost(they are balanced as 280mp unit and reinforce as one, only their initial price is 320).
They had to be delayed/prevented from spam, because counters couldn't arrive fast enough with long T1/T2 build times, since that is no longer an issue, I see no reason why they should still cost 320.
I do know that some top players/streamers say they are fine at 320mp, but I don't see them becoming OP at 280 anymore.
And the same applies to penals, they are not performing up to the cost, so their cost should drop or performance should increase.