Nudity and sex are overall far from gratuitous in BG3.
Of course it is gratuitous. As has already been stated, remove the 'romance' and sex and it in no way affects the main plot and most of the time it does do much for the sub-plots. The hobgoblin back-scuttling the ogress in Act 1 is there for why?
Oh I am prepared to accept that one as a pure joke However to make your point better, show me any part of the Shadowheart storyline that really changes if you do not have sex. How about Gale?
Sex and sexuality sprinkled lightly into the game context can add spice. In my opinion someone thought dumping the whole container of salt and adding a salt lick to the stew was a good idea.