I dont think anyone is saying Obsidian mislead us about being able to romance Eder specifically. However, they chose to include romamces and also chose to deliberately exclude him and gave a lame excuse in game too. Hes the obvious choice for a romamce and a lot of people wanted and expected it. I honestly dont think it matters what the writer wanted to write. This is a product for consumers, who also happen to be backing the developmemt.
If you have a female character and want a straight romance what are your options. Serafen isnt a full romance, Tekehu was in my party literally 5 minutes and I already hate him. And Aloth? I feel like that would be like romancing my brother. I only see him as a really good friend to the watcher. Eder should have been included because its the only one that makes sense or gives straight females a decent option considering he kind of hit on you in the first game too.