Well Steam account is just to buy the game. They need people to use Patreon for the H-content cuz i doubt steam allow those content.
But the real problem is the online mode, which most core content will be and those data will be inside the server prevent any kind of cracking or offline server emulator (unless somehow you have the core data). Now what next, is the double account system:
1. Assume we only need a Patreon account to play without the need to "pay" first. You buy the game through steam, but you still doesn't actually get all the content you buy cuz the data still inside the server. So when they shut the server down, it will be a trash leftover and you can't play the game anymore, so.....what, you buy the game and you suppose to play it but being dependant on a server which threaten to be shutdown and lost that money for nothing because you can't play anymore. At least when you buy an offline game you can play it anytime, and online game are free to play with optional microtransaction
2. Double Paywall, you need to buy the game through Steam and subcribe with money through Patreon account to play. This is the worst monetization pratice
3. The only good path is like League of Maiden, Steam is free and Patreon account is just for optional microtransaction (buy costume, more pose, sex animation,....). Or they goes with offline model most company currently follow is buy a full game and optional microtransaction (DLC, Update patch,.....) with online mode, but this kind of thing can be easily crack, and i doubt they want to pay for DRM. Thus the online model with most core data in server to prevent cracking is understandable, but if they goes this far to prevent cracking, they will never in hell give the game free on Steam, so.......this path is out of the window, to the abyss.