Steam is always one version behind the patreon oneIt is, yes. Basically. Steam just gives you gamer score for your achievements.
I'd however personally say: Wait with buying until you can be sure the game will contain what you are purchasing it for.
Like, I'm still waiting for around 80 % of the promised content xP
Though, if what you are after is currently in the game: Then yeah, you can go ahead as it is very certain more of it will be added.