Well, think about how many types of bread there are. Now, apply that to gender and sexuality.
The problem is because the term 'friendzone' implies that the only worthwhile relationship you can have with someone is a sexual one and if they knew a sexual one was never in the cards, they wouldn't have bothered at all. It's really a wretched thing to feel, like someone is only being nice to you because they eventually want in between your legs and if they knew that wasn't on the table, they'd have not even bothered doing that in the first place.
I don't see how it implies that frienship isn't worthwile. For people who want something more, of course it isn't going to be as worthwile, for them.
I also don't see how it implies that people are only being nice in order to get sex, that's an assumption and nothing more.
I'll give an example from RL. When me and my gf thought the whole "race" thing was something we thought we couldn't work around (Her parents didn't want her dating a "white boy") I said something along the lines of "I still want to be your friend, whatever happens." to which she replied "No, I f that's the case I don't want to be around you, having these feelings and not being able to do anything about it, or seeing you with someone else it would hurt too much."
Was she feeling entitled to sex? Or only being nice to me because she wanted to get into my pants?