Well, I don't know that I agree with the general statement either. Consider ORS alone, Seymour isn't a compelling villain either.
Fair enough, Cindy does end up rushing into the modelling thing. If all NPC's had variable routes similar to Holly maybe some alternative outlet could have been explored.
I mean, it's not like I'd claim Eva is a master of script writing, but for what it is, yes I generally think Ian and Cindy have fun interactions. Ian can be charming or more overt or even put off by Cindy's traits. When they do get together I think their sexual dynamic is fun because Ian can stumble here and there if he pushes things, but playing his cards right he can get Cindy to lower her barriers to do new things.
And I will freely admit that I am perhaps a bit too into Cindy. I don't really find your view disagreeable, I can see how Cindy's scenes wouldn't work for everyone.
At the end of the day all the characters and pairings are subject to individual preference. I don't enjoy Ian/Lena so I wouldn't mind whatsoever if Eva neglected that route wholly in favour of spending dev time on the routes I enjoy or the potential routes I would wish to start.