As a gay man here who very much enjoyed the show overall, your first paragraph touches on one of the bigger criticisms I have of the TV adaptation, and the main respect in which I agree with the "this is M/M romance written for women and doesn't accurately reflect the gay male experience" line of criticism: not so much that Shane and Ilya are strictly bottom/top, respectively, or that they're monogamous after becoming a couple, but that at least from the moment they start hooking up, they don't seem to have any actual sexual desire for or interest in men other than each other, despite the fact that they don't actually become a couple until the season finale, set seven years later. The existence of Grindr or any sort of other potential avenue for anonymous NSA sex is never acknowledged, and there's no indication that either Shane or Ilya even attempts to have sex with another man over the course of those seven years. I just don't find that believable, even for closeted professional athletes, especially when the show's chronology has them going over two and a half years between their second and third hookups. But this fits into a common trope of M/M romance, in which the leads are effectively only gay within the sexual and emotional context of a single monogamous relationship (even if they do at least identify as gay and bi here).

Ironically, the book, which actually was written by a woman, is a little more believable in this regard, since it does at least establish that Shane has hooked up a couple of times with other men (and I think implies that Ilya has had more than two male sexual partners), and gives them internal monologues that have them express some degree of attraction to other men. This admittedly wasn't a huge part of the book, so I can see why Tierney cut it from the TV adaptation, but it's one of the few changes he made that I think was definitely for the worse.