I think that's a bit of an oversimplification of her character. It's obvious from her later conversations with Axel, that she was a very naughty girl with him, even if she didn't behave entirely as a slut. Also the way Ivy describes her, in their conversations, suggests Lena has been promiscuous in the past. So even if she's not been the out and out slut she's becoming on certain paths in this game, she's definitely had a somewhat slutty side since she was a teenager.
I also think the reason she starts the game the way she does, is because after the shock of discovering that Axel has betrayed her, she's lost a lot of her confidence, and believes she needs to be with someone who's very different to Axel. Which is why she's so attracted to Ian. Because he starts the game, as the polar opposite of him.
Also, I wonder whether your suggestion that Lena's slut paths are poorly written and uninteresting, maybe has something to do with your possible lack of interest in such routes?
All interesting points. The problem with most of them is what I explained before: a lot of players assume some facts are canon while they are not.
Re. Later conversations with Axel: not canon. If she does not meet him, and that Ian does not ask an explanation about Cherry, even the threesome Axel/Cherry/Lena has not happened, in that case Lena even says Cherry and her were "never close".
Re. The way Ivy describes her: not canon. On vanilla paths, she even makes fun of her "goodie-two-shoes-style", asks her if her fantasies are still so boring and vanilla, if she refuses the smoke Ivy recalls how Lena was a nerd never hanging around with the others and immersed in her books.
Conversely, I fully agree with your second paragraph. Yes, it is credible that she has lost self-confidence and your point is even more valid when you read her inner monologues when she breaks her dryspell with Robert then has a ONS with Mike ("you still got it, more than ever"). The problem is how it is developed from that point. Also fully agreed on Ian being the opposite of Axel early in the game.
Finally, about your final question, the answer is a hundred times no. TBH, I have discovered the vanilla path only a few months ago. I was going full she-bang first, to the point I could never get Ian and Lena to seriously date as they were both banging everyone, but I was seriously starting to lose interest because of the writing, and Lena becoming a more and more superficial character, then discovered the cuck route, which I thought could be credible due to both their background and could lead to an interesting development, however and even though I have nothing against slowburn, this is really, seriously slooooooowburn, and the dialogs are starting to get repetitive and bland. Moreover I have found this route to be rather depressing, and I play ORS to cheer me up during my breaks from work, not to get depressed.
To be completely precise, my favorite path is not the "pure vanilla" path, I just say this is the best-written path. My main playthrough starts Vanilla but intends to lead Lena & Ian to a loyal swinging route.
