I like the character of echo and appreciate the change she goes through on the show, but I hated her with Bellamy! I just felt it was dead awkward and forced on the show, I kinda felt all of Bellamy’s girlfriends were
personally I agree, (and not just bc I'm a bellarke stan).
I think echo suffered from bad writing which made her difficult for people to like her. the writers never showed the development of her relationship with Bellamy (except for that one scene in s7, which was super weird tbh), and so people struggled to connect to their relationship. I think maybe that more people would have been receptive to Becho had they done a better job at developing them. there would likely always be people that hated it, and that's okay and totally valid, but I think more people would have been like "eh whatever" about it if they had shown us more of their early relationship.
we got to see some of Clarke's developing relationship with Madi, and we got to see her desperation before meeting Madi, which made it easier to understand the closeness of their bond. we got to see some of what went down in the bunker, which made it easier to understand how octavia became blodreina. but we never got to see any of their struggles on the ring. the last time we saw echo and bellamy, she was cheating in the conclave and attempted to kill his sister for a second time. I believe they could have had an interesting enemies to lovers style relationship if they had done better developing it.
also, you're right about bellamy's romantic interests. they were all super awkward and strange. regardless of how you feel about bellarke, I think we can all agree that bellamy and clarke have some sort of deeper connection. you can interpret that as friendship or romance, but there is something between them. the writers never tried to develop a similar something between him and his other romantic interests, which made the relationships feel flat. both of Bellamy's girlfriends really only served as some sort of plot device.
Gina was only written into the show to be killed off, thus deepening Bellamy's trauma and explaining his decisions in s3. echo seems to be more of a tension starter between octavia and bellamy in s5. it was another way for the writers to show that the Blake's are different and now they're at odds. hell, echo spent most of s5-7 separated from bellamy. and in season 6, I think the writers forgot they were even dating tbh.
anyways this got super long, but thank you for making me think anon! at the end of the day, I think echo is an interesting character who didn't get developed very well. she has a lot of hate directed her way, some of it justified and some of it not, but I hope people realize that most of the awkwardness of her character is bad writing. the same way that most people say s7 Clarke is out of character and they don't recognize it as her, is the same energy that I think they should extend to echo too. she has an interesting arc as a whole, I think people just forget it bc they hate her relationship with bellamy. which you are well within your rights to do, of course, I just wish more people would step back and appreciate her character more, independent of her relationship!