Bro, Shepard is already self insert, why would you create your own inferior one...
Every created (and normal looking) Shep is superior to the basic ones, those were made as the basic-bitch character for people who for some reason can't be bothered to create a character in an RPG. I'm guessing you can self-insert into a character that was pre-made. Good for you, i personally can't, especially not a dude, that's why only character creator games are real RPGs to me. Wouldn't make a difference what the main guy looks like, if he's pre-made, it'll always feel like i'm just telling HIM what to do, and it's not "me" that's in the game (that's why i can't get into The Witcher for example). Also, i absolutely HATE the default Shepards, they look too good, more like supermodels than soldiers. Especially male Shep, i don't know why but there is something about him that pisses me off every time i see him, and i'm hard to piss off. And if you put default female Shep next to Miranda and ask someone which one is the supermodel, i guarantee at least 90% of them will pick Shep. Their design is ridiculous and meant to capture players who want to see a stereotypical chad or a hot chick straight out of a fashion magazine doing cool shit and whatnot, even though they couldn't look any more out of place (except the people that make their Shep look like a green goblin, not sure which is worse). Players that are real fans of ME and really want to be immersed make their own, normal and actual soldier looking character. But also, how would playing bro Shep make sense when fem Shep is already in the game? Even if he's not actually Shepard and just looks like him, you can't simply look at his model and not see Shepard, can you? MC could look better, but if i'm brutally honest, i don't care, it's a male protagonist porn game, the MC is his penis.