>>58593962 (OP)
When determining what should be available to a player, Champions on console will read the Switch's save data to see what Megas you've obtained in LZA, and will unlock them accordingly for Champions.
And in many cases (ranked rewards, DLC, etc.) they'll be completely unobtainable in Champions if your save data doesn't mark them as "obtained" in LZA, whereas others you'll have to cough up the VP for those Mega Stones while having them in LZA makes them available for free right away.
My source is that I made it the fuck up, but if you aren't expecting this kind of approach to necessitate the purchase of LZA and participation in FOMO events in order to be on top of the competitive PVP scene in Champions and have a winning chance in VGC, you're a fool.