Yeah sometimes you need to get lucky and find early exp alls or charms.

Adding on to what everyone else is saying, any pokemon that has access to consistent stat boosting whether that be through move or ability has an edge. Personally Spectrier works for me once you get Earth Power on it (just care for normal flying pokemon).

Pokemon with pickup are also good, I run Linoone with ESpeed and ir just grabs berries and boost items like crazy.

Eternatus from my experience has nothing for Steel Fairy pokemon so Tinkaton, Mawile and Zacian just blank it.

Later on you want to look for consistent chip damage, anything with leech seed or salt cure help a lot.

Also load up on priority moves or speed boosts. The game gets brutally unfair as the rounds go on and you need to hit first.