The only thing I would have personally changed would be that Clark would be left as the last human in existence on Earth. No dog, no friends deciding to come back, just Clark reaping what she has sown. She started Season 1 Episode 1 as the savor of not only The 100 but of the entire human race, yet as the show progressed she got consistently dark and corrupted. She literally committed genocide of an entire people because she felt like she had to in order to save the people of the Ark which was relatable and there was justification there in that her people were being kidnapped and tortured and killed without regard and when given the choice to stop, they refused. Contrast that moment from earlier on to the later seasons and ending where Clark is literally killing friends and people she never met at will because she wants revenge for something or because she believes she needs to protect XYZ at any cost like Madi whom she was smothering and controlling for her own selfish reasons. Finn went down that path in the first couple seasons and ultimately realized his sacrifice was needed to atone for what he had done in order to save the people he loves. For Clark, I feel like the ending kinda ruined that and her character progression by giving her a happy ending, even if it can be seen as somewhat bittersweet. Her biggest fear was being alone and Alien Ghost Lexa should have told her that everything Clark did to get up to this point resulted in this moment and in Clark spending her last days being alone as the only human being denied ascension.
Bellamy, on the other hand, was the exact opposite. While Clark in S1E1 was the selfless one and pegged as the savior, it was Bellamy who was the selfish one who would literally do anything to protect his sister and whom literally sabotaged the groups overall well being and even surviveability numerous times in order to accomplish that. While rushed, his pilgrimage on the alien planet and his sister going full cannibal opened his eyes to the truth of Cadogans teachings in that obsession of love leads to this destructive path and how only by letting go can one be truly saved.
From what I understand there was either an issue with Bobs personal relationship with the show runner or something else happened, but I read somewhere that the show runner is claiming that once the first episode of the final season was in the middle of production Bob approached him saying he wanted out and/or a vastly reduced role in the final season which resulted in a change of everything. If true this is a damn shame, as I feel like a better ending and one that would have really redeemed much of the low points of this show would be one in which it is Bellamy, not Raven, who inevitably takes the final test and passes. Out of everyone on this show and out of everyone from the original 100, Raven being the one who ultimately helps to win over the aliens felt completely and entirely out of left field, especially considering her history is not far off from Clarks and a few episodes prior she literally sacrificed the lives of people because she was too afraid to put herself in harms way. If not Bellamy, it should have been Murphy.
That said, I also would have been really happy with an ending that resulted in humanity being wiped out and turned to stone after Clarks final murder.
