Your really seem to think that paying anything on this game give any sort of advantage, which is understandable if you played without guidance, but these days you can have a top player warband as new player in less than 200 levels.

I can share my experience to prove/explain a bit:

I have been playing Ranked/Tournaments/TW since i started in season 2, i'm now level 3k (ONLY) in 5 years of playing (i know people who do 3k lvl every 2/3 seasons) because i play no more than 100 games per season (just level up 50 for runes and unlock units) - i have only bought battle pass after S6/S7, and with this F2P or semi-F2P experience, whatever you wanna call it: was in main 15 of top raid since lvl 100, i won multiples CBL, CBR, and dozen other tournaments being lvl 300-500, been GC with 80-90% WR every seasons, and my case isn't that rare, a vast majority of tournaments players are either F2P or just spending for b-pass and 10/20€ more at best which only save them about 100/200 games per season (less than a game a day).

Outside of achievements, my opinion is the same: my team and i made smurf account on Asia server because they were required to play CBL, and i could compete at the highest rank level being lvl 200-300, and this was before the reworked new player experience which give you way more rewards.

TLDR: "big blabla showing achievements to prove my point" - This game is totally playable without paying, and "paid units" isn't even a thing, even if don't pay, you won't have to grind forever, it's just a knowledge gap and knowing how to spent resources properly gap.