BB was NTR driven from the very beginning. Yes, a lot of noise like the one you are generating now happened after first releases, and Dark Silver had been forced to add the route without Eric. That evolved into Glamour game, and you can see how pathetic that game is. Just admit it, without Eric, BB universe would have died before anybody would have noticed it.
Actually people say that Glamour is good these days, but honestly I didn't try it, so I can't say for sure. I looked into it a couple of months ago and it was not half bad, looked solid.
If the game would have vanished without Eric we can't say, that can't be admitted. Marvel holds all the copyrights on the "What If ..." stories. No, I think there were two points that made BB successful. First of all the incest theme of course, you could only find that in aif text adventures at that time. And then it was one of the few visual games, that were not based on Hentai but had a western touch, that was kinda rare back then. And it was not just a VN, that also made a difference.
Most content in BB had nothing to do with Eric to begin with, so in different playthroughs it didn't really make a difference if he was in the house or not. He would just block progress on certain days. There was no route without Eric, all possible routes included him. The content that came later was separated from Eric, there was no option to have him in it. The war path was the only one with something in it, that could be called NTR (not just sharing or watching another guy) - and that was avoidable by beating Eric when it came to buying gifts for Alice. All the rest was not NTR at all.
The main problem with Eric was how fans saw him. The fan art often depicted him as being abusive (espescially when it comes to Lisa). I am glad that only made into the game in form of fan mods. (note: The BB remake has a Eric storyline, if you want more Eric content, that's what you should play).
BBs big problem in my opinion was that the plot for Anns storyline was complete shit, from the carpal tunnel syndrom to porn movies it was the same thing over and over and over again. It was all about getting from one porn movie scene to another. Ann was all too dumb to be halfway interesting, all her content was about controlling her which is only entertaining for so long. The girls need their own agenda in order to stay interesting, that worked for Alice, not so much for Lisa who was also reduced to that teen that needs sex lessons at night with Kira ... that was afwul, but not as bad as Ann's content.
And the game was designed too simple. Once unlocked, you could repeat a scene over and over again ... or not. It was always the same 4 or 5 images.
Alexey is doing a much better job in bringing variation to the game, all scenes are a lot more elaborated, offer several options to continue, you have a LOT more variation in spying / changing scenes and similar stuff, the environment feels a lot more alive than the original. And all that has nothing to do with Eric.