If I was running the backend for a game like MTGA, I would definitely find value in having a few of those kinds of accounts hanging around. As long as they don't terribly break things, you can use them to discover performance and scalability issues. If anything, I'd probably pull additional telemetry just for those accounts specifically.

I'm generally a proponent of soft limits on almost everything. It's better to hit some artificial cap than to end up chewing away on a transaction forever or crashing some service that can't allocate the memory to deal with it. In this case a limit on gems in an account, packs in a transaction, packs in an account, etc.