Thing is, I don't think they are all the same even if they can all be romanced by both genders.
Cassandra's personality is what it is. Her preference for men or women doesn't impact that. The same goes with Sera and Cullen and whoever else is/may be a love interest. What's going to separate these characters is their personality, not which set of genitals they prefer.
Yes, but I would argue that sexuality does affect how you interact with others. If you are into someone sexually, you will behave abit differently towards them than vs someone you have zero interest in. Not in any extreme way, of course, but still.
I see your point, though.