Hypothetical sitation: you are joining a new campaign in which all other factors are positive (you know the GM and group, it's in a setting you like, whatever) but there is one hitch: race/heritage/species is cosmetic only.
I mean, I stipulated that everything else was positive to you, so it's up to you what edition and world you are answering from.
These statements seem at odds with each other. You can't really change something like that and not have larger changes to the game.
On the one hand, I'm 100% fine with a DM who is very restrictive about character creation. "You're all humans" or "Elves are kill-on-site by other races" are the type of world building I can get behind at Session 0. From that standpoint, it doesn't sound like there would be a problem.
But, if I'm choosing the edition and world... Let's say we're playing a 3.x OA/Kara-tur campaign. I say "I want to play a Hengeyokai on a personal journey to connect with my animal self". The DM says "Sure, but mechanically, they're the same as a human". Huh? Their alternate form is literally turning into an animal. Does that mean that, in this campaign, Hengeyokai don't have the Alternate Form ability? That normal Hengeyokay do but I don't? That I can turn into an animal, but still function exactly as a human? Even if I'm a small sized carp, or a crane with a fly speed, it's "cosmetic only"? How the heck is that supposed to work?
Okay, that's an extreme example. But what about undead races? Warforged? How can differences like breathing and sleeping be "cosmetic only"?
Let's go even more basic. I'm a human scout. I see a Goliath fighter. I ask the DM to try an assess what kind of a threat he his. The DM says he apears to be about average build for a Goliath. What the heck does that mean? Should I expect him to be stronger than a human, using larger, more dangerous weapons? Because Goliaths are obviously stronger than humans and use big weapons that do more damage. Or does average build for a Goliath mean he's the same as an average human?
Honestly, this just sounds like a mess. Easier to say "Everyone is a <insert race here>" than to say "It's cosmetic only". I can get behind the former. The latter would take a lot of work. And if the DM doesn't have an immediate answer worked out for the questions, well, that's a sign the DM really didn't know what they were doing.