Which is what my post was in regards to way back when, yeah it nice that some of these side girls are getting designated paths and it's nice that they are getting endings.
But ultimately they are a means to an end. The MGs are getting the story, so to speak. These side girls bar Zoey who has had hers might get nothing more than "we've been foolinf around for a while now let's take it to the next level" before ending.
Obviously we don't know shit, but the argument that there still be a load of content because side Girl C hasn't had her moment yet or Side Girl D has only just realised her feelings for MC is a weak one.
Agree 100%, the only thing I would add is I do believe that DPC will flesh them out a bit more than that. He might not of course, like you said, we don't know, but I think they will have a meat on them (for the higher level SG anyway). Quinn is a good example, there is a whole storyline dedicated to her this episode that you only see if you are on her path.
But the biggest difference is that the 5 MG are crucial to the overarching plot and you will continue interacting with them until the end. None of the others are, you can reject them and they basically disappear. If you're not doing a Quinn path, you can go this entire update without saying a single word to her. If you deny Zoey, you never see her again this episode.