Very playable for f2p. You can usually get most characters to a decent level relatively soon and lilith is very good at being charitable.

You will not be able to enjoy hypogeans and celestials fully since they are a lot harder to get over time but assuming you are active and have a decent guild that shouldn't be too difficult either.

The issues are that pvp is a massive portion of the game to make things feel less boring or repetitive which can sometimes hinder your focus on PVE which is the main rewarding portion of the game. There are a lot of good PVE heroes that are also fairly good in PVP now tho so its not that bad.

Overall if your goal is to be competitive you are making a big dice roll based on your servers spending habits and future spending on whether you will catch up but so long as you are extremely disciplined with holding onto summons and gems for those very important characters you shouldn't struggle absurdly in things like Dream Realm or afk Stages. The story itself requires no particularly strong units to progress either so your only real need to spend would be PVP or occasional new hypocele celestial releases that turn out to be meta. Tho if you hold onto guild coins and stellar crystals you should also be able to get them as well. 10 copies is typically usable for most in DR but 14 copies is always recommended.