The companions being playersexual is a reasonable compromise in terms of game mechanics. With the number of companions they offer, they can only present so many choices to each sexuality. My personal preference would still be a set sexuality for each companion, but I can see where Larian's design decision is coming from.
What is true, however, is that the character's attempts at "romance" are coming out of nowhere for the most part. Lae'zel is especially guilty of this. There is no real setup, no arc, it's not even tied to approval level or exploration of her dialogue tree. And the post-party scenes for of all of them are largely awkward and poorly animated on top. The entire experience is jarring at best.
The best out of the bunch is probably Shadowheart, because she doesn't immediately want to jump your bones after a few days and what is barely the beginning of your adventure.
It's actually genuinely surprising Larian went for this, considering that even in DOS 2 the sexy times were the culmination of the romance arcs for their characters.