I feel like there's a certain 'type' of character that gets comparatively far more content, mostly due to author appeal and such, that's definitely fair to say. Female Naleen in particular was magnifique back when TiTs first came out, and level 2 was locked behind hordes of spooky jungle monsters, when getting constricted by a naleen was basically GG (And before the separation between 'deep Mhen'ga' and 'normal Mhen'ga' as I call them. You just hoped you ended up fighting more zil than naleen, since zil were a far safer encounter. I still go back there on my level 8 Steele to look around for what I head-canonically believe to be the same female who waits on the outskirts of town in the bushes right at the edge of the jungle, waiting for that human to return so she can try to catch him again... or be caught, :3 If somebody ever wrote an xpac to turn her into a proper NPC with a name and all that... instant waifu, no questions asked.
Compare that to 'random generic NPC who (BIG SURPRISE!) has a dong hidden under those flimsy clothes. I wasn't at all surprised upon my first encounter when the Mhen'ga Tanuki xenobiologist had a dick. Just give us some vanilla ladies, and some vanilla dudes. That would be THE BEST. futa density is currently way too high. Or at least, bare minimum, build in a way for Steele to influence gender a bit, like Embry. If we can have Penny doing illegal drugs to grow a dong, what exactly is the moral hang-up to injecting other drugs to turn dudes into ladies, or removing undesired genitalia? Ignoring real world morals and such for a moment, these aren't real people. If someone wants to give Burt a pretty little human pussy and make his cock vamoose, why not? Other than 'because nobody's written that content' I mean. Something similar-ish was done with Kelt in CoC, to varying opinions, I just think that current characters who get written and accepted in fall into the trap of 'I need to have all the equipment to please all potential Steeles'
I'm not saying every character currently written is a futa, I know that's a lie. Not every new character needs to be written with the intent of becoming Steele's lawfully wedded wife, either. By and large the characters who invariably get expansions seem to be the ones who 'fit the mold' while ones who don't are one-offs.