Tactical flexibility
Terrible on the move
Cannot build free sandbags or trenches
Grenade that doesn’t help when flanking or against charging units
Poor survivability
Infantry sections are worse on the move.
Pio can built sanbags and come in T0. You have sandbags event before you have gren.
Rifle nade have longest range of all nades as a trade off. Gren doesn't good when flanking because they are not designed to do so.
Also, gren come with fause while being cheaper than sections, and they receive weapon upgrade right on the field.