I don't know if people knew this here, but if you followed or subbed to his patreon you'd know that the dev had some issues, mental and family issues if I recall, and he stayed away from the game and patreon for more than a year so this game shouldn't even have a chapter 3, but then he came back and started working on it again. I'm not here to defend the game cause the ending really was bad and rushed af,but in my opinion the dev just wanted to get rid of this and move on to do something new, with that being sad, it'd be better if he just abandoned this game and started working on a new game instead of doing what he did.
I agree with you that given his situation it's remarkable that he wanted to give some kind of closure to this game. But as you also said, it would have been better to just leave it abandoned than give the ending it has.
I remember a couple of other games that went through the same kind of issues (dev with real-life severe/critical problems), yet they managed to give them good enough endings. Maybe a bit rushed, and maybe they also left a few loose ends, but the main arcs were closed properly, and the players didn't end up with the overwhelming feeling of frustration/disappointment this game has left most of us.
If you look for games like "Babysitter", or "One Lie" you will see cases where they preferred to take either a long time before giving an ending or giving it a rushed but appropriate one.
If you look for "The intoxicating flavor" you'll find another game with good development but where the dev preferred to leave it as abandoned rather than giving it a crappy ending.
It's a matter of perspective, I know, but IMHO, If I had invested as much effort as I'm surely this dev did, I'd rather freeze it until I have the bandwidth to finish it as it should rather than create such poor ending.