They are the same cost as storm troopers in coh 1. Which is the same unit essentially. It's not pg under performing, it's grenadiers over performing.
It was never a problem during the Soviet T2 meta, when you could use MG's and Mortars without worrying about M3 spam although double Sniper was still a problem. Even when they have 1.2 armour nobody complained about them or Grenadiers. Now that they're too squishy to do their job (which nobody can agree on what their job actually is anymore), suddenly Grenadiers are OP?
Yeah, no. And if you want to nerf Grenadiers so hard, I hope you also plan to nerf everything else to balance is out, otherwise Ostheer will be in for one hell of a ride.