Very p2w if you want to be competitive. You have nothing to lose by trying the game out. If you don’t like it don’t play. Game is p2w to be the best. I’ve enjoyed f2p playing since it opened. Personally I find the game rather enjoyable and don’t care if some whale is on top of a meaningless list.
I think P2W is 8/10 which means heavy p2w. You can buy pet boxes which save tons of time considering how crappy pet droprates are (and are locked to daily mission which can be tried 1x per day). Cosmetic stuff that actually give small stats are locked behind paywall, but this is not the worst. I think worst thing are these red imprint scrolls that can add 3 extra stats to your gear if you are lucky, if you spend 200 euros on them and constantly use on an item until it gets top tier bonus combination then you are ahead in strength.
That said, you do not need to be waller warrior for just finishing or doing good in pve content, but if you want top scores in daily dungeons then it helps. Also you will suffer in pvp where some people will just buy thousands of special premium hp potions that are on separate cooldown. They can be slowly obtained without paying but wallet warriors will have them in ridiculous amounts.
You also could sell items for redzen to get free “premium currency”, but that functionality got at least temporarily removed due to botting and I do not know if it will come back. Even then, player who pays and sells items can get much more redzen points than the one who just sells items. You progress much faster if you get plat, more runs per day, instant travel/shop anywhere. But if you’re starting now, you will never catch up to those people who already p2w because they are try hard in the rankings.
Pets with attack stats (and in best case +10% (and upwards) more soul exp – in garden you only get kobold and larva, which are bad (but they give +Zen stats) and huge boost to combat power (not mandatory now, but later you need 180k min for 3 dungeons). You want the pet that gives attack and beast damage. Bear in mind that if You need MU Legend Zen, you can find and buy in U4GM.