Well, first, I don't consider Riza's characterization in the manga faulty, as in being bad writing or something. Her characterization makes sense and is perfectly valid. I just don't like the character it makes. Second, love is not automatically co-dependent and unhealthy. Izumi and Sig are devoted to each other but we're not given any indication that they're co-dependent. They would each be devastated if the other died, but we're not shown that they would give up on life and wait to die. Roy loves Riza but we're not shown that he would turn suicidal if she died. He went mad with revenge over Hughes' death, but he didn't give up on life and his goals and sit and wait to be killed. I never said Riza was "weak"; I said she was dependent on Roy. Roy depends on Riza as a comrade and ally but is not dependent on her the way she is on him. Riza puts herself on unequal footing to Roy - she puts him above her - with her co-dependence. Love alone wouldn't do that. Love means we sacrifice ourselves for our loved ones, yes, but it doesn't mean we sit and wait to be killed if we think they're dead. I could just as easily argue that if she truly loved him she would fight twice as hard to see his dream fulfilled after he was gone. Love doesn't dictate that a character would go one way or the other, the character's other traits do. And in this case, it seems to me that Riza's actions indicate an unhealthy co-dependence.

I didn't mention Ran Fan partly because the blog post I was reacting to didn't mention her specifically, and partly because her relationship with Ling was always master/servant. It's unequal by nature and we're never told otherwise. But even so I didn't get the same co-dependent vibe from her that I got from Riza. She's devoted because she loves him but also because he's her prince, she's culturally conditioned to put his life above hers. Riza isn't.