There is a difference, you got more space capacity in the grenadier vest rather than the normal one. I think this is intended. Even with a normal vest, you got pocket you can fill with stuff. VOG-25 can fit in these pockets even if they are intended to store ammo clip at first.
So in the same grenadier vest you can either carry more VOG-25 or get a better mix VOG-25/weapons bullet clips than in the standard vest.

Be aware that if what you asked has to be done, they should have to revamp the inventory and show us something more like Escape from Tarkov where each clothes item got a specific space in square and each smaller item have to fit inside these square, and they push that to the real representation of pocket storage... that would be ideal, but Bohemia is aiming for something more user friendly and not that high hardcore approach.

It seems to me that the games of the Arma series make the player feel like a real soldier.
And for this, realism is introduced, for example, by adding a system of weights.
Now it makes little sense to wear Lifchik - Grenadier, since the standard Grenadier set - 10 VOG-25 grenades fits into a standard vest.

If the developers want players to play certain roles, then they need to add more realism to the inventory system.

Otherwise, we will see a super soldier who is armed with a machine gun, a sniper rifle and a grenade launcher and performs various roles.

Yes, and for this the character has a weight system, which affect the stamina system.

Your capture clearly prove there is a difference. A standard vest will hold 4 VOG-25 (you're counting the jacket & the trouser, they're not part of the vest and anyone has them without a vest...). With the same additionnal gear (clip/grenade), you can load 14 VOG25.
If you can't spot the difference between this

and this

I am pretty sure noone can help you sadly.

Maybe change inventory for that:

If the player wants to be light, they will simply take less ammo