Let's calculate Laser Rifle vs. Plasma Rifle
Laser Weapons + UFO Power Source + Elerium + Laser Pistol + Laser Rifle = 50 + 450 + 450 + 100 + 300 = 1350 (research * days)
Plasma Rifle + Plasma Rifle Clip = 700 + 400 = 1100 (research*days)
Heavy Plasma + Heavy Plasma Clip = 800 + 400 = 1200 (research*days)
So you're definitely right. But I believe that Laser Rifle is better than Plasma Rifle.
Unlimited ammo, costless use, quicker shots (but less precise) are a good thing. Laser Rifle can be used effectively till the end of the game. However one would need to replenish clips for Plasma Rifle.
Against Heavy Plasma this doesn't fare well... that's true.
I personally use this change with conjunction with some Plasma Research changes (
https://openxcom.org/forum/index.php/topic,2765.msg29088.html#msg29088) although I have "upgraded" research costs and manufacture costs by presented ruleset.