I agree allied nades are more cost effective but they use nades far less then axis. This cuz they are either tech or doctrinaly locked. Also sections and rifles are very expensive to upgrade. This in turn leads to less midel losses overall and probably evens out the bleed across factions.
(Edited)
Not really. This grenade sidetech is not always used only because allied players prefer to get AEC, T70, or generally armour as soon as possible. They also prefer not to spend resources (fuel, monpower, munitions) on nades because they can be dodged (to many players weapon upgrades or offmaps are better in the long run). Having a vehicle faster usually will bleed the enemy more reliably and will save munitions on the mentioned upgrades or offmaps. Plus elite infantry units get grenades irrespective of extra tech premium. So what happens is that extra tech can be skipped to have vehicles faster (axis can't really do that) and elite infantry squads will have their grenades anyway.
Footnote: with UKF grenade tech is actually recommended instead of weapon upgrades early game (probably due to their grenade great cost/power efficiency)