While I'm admittedly a fan of immediate (or at least speedy) gratification, a good buildup can definitely make the payoff much sweeter. I do like quite a few slow-burns that handle progress well. Although I don't think every quick hookup has to be one-dimensional - some games have made well-written scorching scenes out of one-night-stands and the like. But I understand not wanting to do that for someone who might be an important character since it limits the progress you can have with their arc down the line.
Thing is, like you said, Eleanore is a MILF at the point of a big change in her life. For me, not having the MC involved in any way at that pivotal moment diminishes his role as the protagonist, and diminishes her appeal as a character, since any interaction with her in the future will just be a reminder that the MC wasn't around for one of her most important moments. There are other games like New Coral City which have a big cast doing their own thing and hooking up with various people, but it still feels like the MC has agency, and is in the driving seat for the most part. Having other perspectives to flesh out NPC backstories can be a useful tool, but it also runs the risk of losing that tight focus required for player engagement.
It's a shame, since the writing was good, and I was looking forward to see where it goes. But when a game hits with a buzzkill this early, it's hard for me to keep interest alive. Worldbuilding is always important, but sex-themed adult games rely as much on the gut feeling (that bonerific appeal, if you will), and it seems like the latter was sacrificed for the former in this instance.
Good luck with the development, though. Always important that you make the game you want to, regardless of what critics say. I can appreciate that not every game is for me, nor should they be.