You sacrifice durability, longevity, ammo choice, and reliability for a reduction in recoil, a lighter rifle (sometimes), and faster split times. If that's what you want from a rifle, then sure go for it.

It's nice on a square range doing square range stuff, but outside of that, it has no practical application.

There is nothing wrong with that, range toys are great, but it's still the very definition of a gimmick.

You can shoot groups wayyy faster if you have a well tuned rifle running LW BCGs..

Okay. Not my thing but sure, it does do that.

If there was a way to reduce recoil without using LW BCGs, then you can debate why those reasons make them a gimmick- but there’s literally no other way.

lol, what? There is a shit-ton of ways to reduce felt recoil. Muzzle devices, weight, adjustable gas blocks, better buffer spring, tuned ammo loads. A LW BCG will make a large difference but it relies on the other parts of the system to be tuned whereas, generally, the other parts in the system can be tuned without being forced to change anything else.