Well again I don't want to get too bogged down into the Doctor Who quagmire so this is the last I'll say on it.
The first 7 seasons of New Who as a remake of the original would have been fine. They are good solid sci fi seasons overall. (Well not so much s1 and 2, but I'd forgive them as teething problems.)
Ultimately however as a sequel, it's never worked, and worse it messed up the classic era in the following ways. (Even if you aren't a DW fan I'd recommend baring this in mind as it shows you how an iconic character can be trashed so easily.)
In Classic Who, though the Doctor changed his appearance, he was always meant to be the same character underneath. Regeneration was like an advanced form of healing. His body broke down, then repaired itself, but in doing so it changed his appearance. His outer personality would also change to an extent too. Still his core persona was always the same, his consciousness was always the same, and all the Doctors had the same memories. As a result all of the Doctors followed the same template as it were, with the actors trying to do something new within that template.
New Who however from the start threw that template out.
1/ In old Who the Doctor travelled because he wanted to explore the universe. He was a scientist with a desire to discover new worlds, new species etc. He also was a hedonist who loved his life. His ship had everything he could ever want, (food, somewhere to sleep. entertainment.) He lived by his own rules, could visit anywhere he wanted.
In New Who he only travels because his people have been destroyed. He says he would much rather have a normal life and settle somewhere, but can't. He isnt really a scientist with an interest in discovering new species, more of a superhero, and is quite mopey. They also later revealed that he never wanted to explore, but fled because of some prophecy, and then after that they revealed that he was brainwashed by the Time Lords into being a hero. (And that the Doctor persona he has, was created by the Time Lords when they brainwashed him.) We also learned that he lived for billions of years before the first Doctor, meaning his current life isn't really important as it's just 1000 years in among billions we'll never see, where he was a different person.
2/ His moral code in classic who was that he would kill if need be, but preferred to find a peaceful solution if possible. He was practical and fair. In New Who his moral code is all over the place. They go too far both ways. In some instances he refuses to let guns be used under any circumstances, literally even when the bad guy is about to destroy the universe. In others he is too vicious, and tortures an alien family for all eternity.
3/ In old who he was largely asexual. He did have a family at one point but he never showed any romantic interest in his companions. He was too focused on his work, often had a more fatherly relationship with them, and was often too old for them. In New Who he is worse than Captain Kirk! His first love interest, Rose, is only 3 years older than his grand daughter!
4/ Regeneration in New Who is rewritten so that actually each Doctor is a different person. When he changes he dies and only the memories go on. This completely ****s up all of his relationships in Classic Who, like with the Brigadier. Before it was one guy's friendship with the Brig, now it's 7 different guys.
5/ The Doctors maturity has also gone in New Who. In the originals series, whilst he could be quite immature in getting his way, he had a mature outlook on the hardships of life. In contrast to say Buffy, he was someone who had lived a full life before we see him. (It's strongly implied that his wife and children are dead, which could also explain why he isn't interested in romantic relationships.) In Old Who he could always cope with loss, would remain level headed in most situations, and never let his emotions cloud his brain too much. (Unless it was the possibility of discovery.)
In New Who he is a hysterical, screaming, immature character, who can't cope with loss of any kind. Whenever he loses anyone he goes nuts, tries to kill himself, carries out a genocide, goes into solitude and in one instance risks destroying the entire universe to save them
6/ Even little things like the Doctors dress sense and appearance. In Classic Who the Doctor tended to wear frock coats, over the top clothes, and clothing with a more Edwardian/Victorian feel to it. He also tended to have big, long, unmanagable hair, all of which reflected his eccentric, man out of time status. In New Who however he wears modern clothing, had short almost shaved hair in his first appearance, and spikey up hair in Tennant's time.
All of this is before we get into the controversial sex change which is a big deal in changing the characters identity. Obvs I'm not saying that a woman can't be a hero (or else I wouldn't be here) or even a similar character to the Doctor, but bringing it into his story, turns him into a Ziggy Stardust type character. A gender bending alien. I love Ziggy Stardust, but that's not really the Doctor.
The Doctor is a stuffy old, eccentric, British gentelmanly hero like Sherlock Holmes. That's what he always was, even in the body of a young man. Trying to make him a sex god like in Tennant's time, or an androgynous, gender bending character who breaks down all gender stereotypes kind of seems silly, when you try and link it to William Hartnell, the first Doctor.
William Hartnell laughing video
Yeah he seems like a real David Bowie type who could get off with a 19 year old Billie Piper doesn't he? He definitely seems like a lesbian icon (which the 13th Doctor has become to some people through her romance with Yaz.)
All of this like I said has taken us to the point where we aren't sure who the Doctor is anymore. I was growing up. He was the eccentric, Sherlock Holmes type hero from space. Now? Is he still that due to Classic Who? Is he a sex symbol like in Tennant's time? Is he a David Bowie androgynous character?
It's going to be quite a big task to take us back to the Doctor, if it ever happens at all.
We cannot allow the same thing to happen to Buffy. Buffy like the Doctor has a core identity that must run through every version or else we are not doing Buffy anymore. Her identity is of a younger character, female (obviously) a bit of an underdog, lives in more relatable surroundings despite the monsters, is quite a tragic character, goes against the partriarchal rules she is bound by etc. (Even the Kuzui movie get's that with the "my keen fashion sense." bit)
Fortunately I don't think Buffy fans as a whole would accept an in name only Buffy, but if it were successful, even for superficial reasons, it would be a worry that Buffy could lose her identity like the Doctor has.
