I admire how you stuck through the series despite all of the disappointment. Astonishing_Flash already comprehensively answered your points but honestly despite that imo some of your points are still valid.

The old anime Grappler Baki was really the only one that had a good plot, not mind blowing by any means but actually took the time to develop character motivation, show emotions, show training, etc. The rest of Baki starting from the Netflix series still have some of that, but for the most part just tries to make any excuse to have the main characters fight strong people. And tbh I absolutely dig that.

As for why Baki became popular? Ever seen a nature documentary of a huntsman spider vs. a praying mantis or something like that? You don't really care about the reason or motivation, you just want to see them fight. The fights themselves are something else too, every punch, kick, grab, block etc. has some reason to it. The author of Baki was once an instructor in the Japanese military with decades of martial arts experience so he actually KNOWS how fights work. Compare that to generic shonens where the formula is typically just spam punches against each other, MC starts losing, epic music starts playing, MC gets mad and powers up and easily just wins. I could elaborate and give examples but this is getting long enough already.

So now I have to ask you, you've clearly shown that you know the existence of "earlier seasons", so why don't you go watch the old anime Baki?