Xi Yazhou did an episode talking about this too:
Basically the example BTGs we saw in action in Syria and Donbass around 2014 were adhoc formations themselves built out of the most elite units of an combined arms army (their infantry units were often VDV or naval infantry for example) and given much higher level of C3I gear than normal for Russia. By Xi's estimate Russia can only put together no more than 10 BTGs to this standard.
The current scale of war has what? Equivalent of at least 30 BTGs in the fight (by some estimates by Ukraine prior to they war they are claiming 60-100 BTGs). That means if you want to have your 10 elite BTGs the rest would be trash tier. So Russia didn't do that and they reshuffled the decks and spread out all their technical assets back into their traditional larger formations. Once you dilute out all the elite units and equipment across a much larger force you will of course no longer be getting your 2014 standard elite BTGs.