If you can keep the sex scenes fresh and interesting, you can never have too much, even in a plotty story (in my opinion). But if it’s just the same mindless banging followed by a quick squirt and rinse, repeat, then it will get pretty old pretty quick. With some writers, their sex scenes become formulaic, and when that happens, I tend to just skim over them or skip them completely. If its predictable and repetitive, it’s not much of a turn on and it can easily feel like ‘too much’ or ‘gratuitous’.
But some people like predictable and repetitive. Sooo… Whatever floats your goat.