you dont have to do much, and if u follow the meta you should be able to win a lot, although there will always be 1 or more players that spend tons to get a strong lineup.
I played in two battle zones, in the first one (11 months ago until march) i was easily top 3 in arena, although i could not beat the p2w rats even after spending 50 euros myself.
now in the 2nd battle zone i am in the top 10 of the entire battle zone, although i’m beat by other players who have spent money, some of them more than others. only spent 15 euros on this account.
it doesnt take much time, to play, maybe 1 or 2 hours per week. and its very addictive. already tried quitting once but i could not help myself after all.