How much of this did you play? Lol. Cathy didn't "let" him do anything. She already had been fooling around with Lydia then points out to MC that Alice has feelings for which the MC reciprocates and the whole things evolves to a nice fuckfest amongst the four. Cathy then wanted to fuck Alice 'cause that's how an open and sharing dynamic works where you switch partners. Everyone's being passed around - not just the MC. You act like she keeps cucking the MC from having any meaningful sexual content when there is plenty of content to suggest otherwise. Your fixation with a female protag being the proactive one in initiating the sex is clouding you from giving any sort of viable opinion and if you think this is the dumbest MC you've ever seen, you really haven't played much at all.
As for the low rating of this VN, the problem lies with NL thinking he could make a kinetic novel this long with minimal choices and expect it to retain interest in the long run. Triangle shows up within the first 8 pages when you filter games by overall rating and all time likes. Why? It was a short sweet novel with a simple concept that had passable renders. Game that was meant to be short and simple had less to criticize and grasp and therefore people rated it well. Then you have this game where gameplay stretches for weeks at a time and in a era where people clamor for choices in their game, intrigue, conflict, and a plethora of tags that aren't vanilla. This game has very little of that and now you stretch it over an extended period of time and people are going to get bored very much sooner rather than later. This game has more than enough H content in it for most people but the lack of every aspect above and the sheer size of it is enough to take people out of this