L65 is useless? I never got that memo, I often carry it, AFAIK its a good alternative to the other 5,56 rifles and better at bursting than most of them. I consider it an upgrade on the MP5.
I do think some guns seem to occupy some weird niche, where they seem to be "stuck" between tiers. AK47 is one example, if you can get the AK47 you can get the AKM. AK47 is mainly useful as a early drop.
I also think its kind of a meta-gaming issue, because early on you're using your few scientists to do actual research not to look at stats of possibly useless guns and see which one works for you.
One idea I had: If we're going to have weapon customization like scopes and such, why not make it something done by engineers? Engineers practically are there only to open ammo boxes and create alien trace flares early on. I guess pretty mundane changes like scopes would't even require special resources, I mean scopes are just scopes.
Another idea I also had was the possibility of X-COM making
Wildcat Cartridges for their own use. Which could end up in some pretty weird and unconventional rounds - like poison bullets, alien fuel tracer bullets, etc. Would need careful balancing, through.