So, what is the idea behind low mass/ light weight BCGs? My first guess is to be able to use an adjustable gas block and turn it down to get more velocity. Am I on the right track? Currently working on a 224 Valkyrie project and those things are all about velocity. So, I'm wondering if the low mass BCG is the way to go.

Lower reciprocating mass = lower felt recoil impulse.

Also changes the speed of the action cycling (faster), and will help some triggers get the most out of their custom specifications.

Less gas pressure (DI) is required to cycle the BCG.

You can play around with these factors to fine tune a specific/purpose-built firearm.

ARs work reliably and with minimal recoil as is. Lowering the reciprocating weight means you need to lower the gas or up the spring weight and this results in less cycle strength and less reliability, IMO. Upping the buffer weight would somewhat equal out the lower carrier weight but then your back to where you started, making it pointless.
An AR has more recoil the less it weighs so lowering carrier weight to drop overall weight is rather counterproductive. The only reason to drop carrier weight would be to drop the reciprocating weight beyond what can be done by dropping the buffer weight alone. This puts us back to upping spring weight or lowering gas.
No harm in experimenting but the ultimate result will be similar recoil with less reliability, IMO.

I bought an AP Customs Rhino LW unit for an ultralight build. Took the weights out of a standard carbine buffer and turned the gas WAAAAY down. Runs on ANYTHING i put through it, has nearly zero felt recoil (noticeably less than a standard AR) and the rifle with irons weighs under 5 pounds. No polymer receivers or LPK, aluminum and steel everywhere but the stock.

Makes an excellent rig for younger, disabled, or new shooters to get some time in with a semi auto who may get fatigued sooner than a seasoned shooter.

I have a low mass BCG, adjustable gas block, light buffer/spring in my 3Gun rig.

Those combined with a good compensator do a lot for recoil & muzzle rise. You can see the effects in split times and shot dispersion.

It does work. An additional benefit to the AGB is action stays cleaner.

3 gunners started using lightened BCG's to reduce recoil impulse so they could get on target faster when running through a course.

Increase lock time with a heavier buffer and/or carrier for your purpose of increasing velocity would be your best bet IMHO.

Using an adjustable gas block and turn the gas off completely and manually cycle rounds would likely give you the most velocity, but it negates the purpose for an autoloader platform.