I came across an article a while ago in which the author argued that Friends was a show about how Ross was the hero, and was gradually made dumber by his social group over 10 years.They brought up examples of how, when Ross would talk about work or discuss a topic where he was proven to be intelligent, the others did nothing but mock him and make him feel lousy for being smart. And, like you, they pointed out how Rachel basically just turned an already damaged Ross into an emotional child, who would run back to her because she is an evil bitch.
It funny how we can, indeed, point to Susan (and her partner, who hated Ross for no other reason than he was a man, referring to him as nothing more than a "sperm donor") as being a major catalyst in breaking Ross. Yes, we see in many flashbacks that he always carried a torch for Rachel, but he was living a good life, married, child on the way, and a great job. While our attitude toward Susan is painted by archaic writing (making her and the partner - what the fuck was her name, Carol?!? - little more than man-haters, which was common for the time the series started), it still stands that she as a character is terrible.
I'm not a fan of the last couple of seasons, mostly because most sitcoms seem to have a shelf life, and then they decide they have to shake things up to stay "fresh". Like many sitcoms, characters started hooking up with each other, then kids are added, jokes become stale, and suddenly, everyone's trying to figure out why fans aren't watching like they used to. I still think there's something to the British attitude toward television, where you do limited series, instead of endless seasons of 22-plus episodes, where writing can suffer for the sake of advertising sales and talent salaries. Of course, if a producer would like to pay me a pantload of money to do such a job, I would sell out like Gene Simmons and take the money.
Of course, without the misogynistic and conservative diatribes.