It wouldn't be so bad if the fandom's(/industry's?) taste for what makes an "appealing" character weren't so narrow. It's mostly slight variations on a basic template of "young attractive girl/woman with one or two special quirks, or maybe a unique theme or aesthetic, to try to make her stand out" + a generally nice and appealing, but pretty generic voice mainly suited for pop music. And even the relatively few characters who do fall outside of that still tend to be generically attractive, usually pretty young, designed for "wide appeal", and drawn in a kind of "industry standard" anime/manga art style. It is in fact very similar to idol culture and gacha games, where characters are designed first with marketability in mind, rather than... any actual character.
At the same time though, I don't think vocal synths being "character-based" is at all a bad thing, inherently. To me at least, it just makes sense to put a face on an instrument that's meant to imitate the human voice, just like it makes sense to put a picture of a guitar on the box of a guitar synth. And for all I badmouthed generic moe teen girl characters in the previous paragraph... I actually really love a lot of characters that fit that mold. I'm really looking forward to Natsuki Karin and Hanakuma Chifuyu, and Karin's voice in particular I find to be very cute and charming; I think her nasally-ness gives her more character than a lot of other synths of a similar type. And she has a weird little demon rabbit plush companion thing! I just wish more vocal synths would be a bit more adventurous in their characterizations.
I've seen people respond to complaints like these- basically wishing for vocal synths to cater less to moe/anime/otaku/idol culture and not be seen as just a "weird anime thing" by the general public- by assuming that we want to go back to the days of like, Cantor and early Vocaloid; where you either had completely faceless and characterless synths, or at most a stock photo on the box. Or worse, that we are as actively disdainful of the fandom as EmVoice is. As if there's no room at all between "cutesy moe idol singer anime girl in a high school uniform" and "no-fun-allowed, business only, super professional virtual instrument with zero character". As if "anime" is the only art style capable of creating fun, appealing, interesting character designs (and yes I know "anime" isn't itself a distinct, coherent art style or anything, but just try and tell me you don't picture a certain type of artwork in your mind when I talk about it this way, in this context).
"Less moe synths" doesn't mean "no more character synths", it just means give me something new for a change! Give me character designs with actual character, not just marketability! Where the design decisions are made not based on what you think will most appeal to idol otaku or "whales", but on what makes the most sense for the voice and character you're trying to create. Hell, give me something that looks like the fella in my profile picture; I'd lose my shit in the best possible way!
On a completely different note, I am now downloading Myriad Harmony Assistant. Thanks for reminding me it was a thing, and that it's technically free.