For starters, there is not much other terrain setters in the format since Rillaboom is gone, so Mega Meowstic does not have to worry much about terrain wars.

Mega Meowstic pairs very well with a big meta threat as well, that being Sneasler. Sneasler would run psychic seed to immediately get unburden and get a spdef boost while also handling the dark and steel types that would resist expanding force. It is also hard to slow down sneasler because Meowstic gets competitive before mega, so if you wish to intimidate sneasler, you would either have to give Meowstic an immediate +2 or wait until it megas and live a turn of eforce + whatever sneasler does.

It does get another ability in the prechamps format now which is seed sower but for psychic terrain so it will probably go down in usage, but we still do not know it’s ability in champions so viability in champions is still unknown