On the aspect of difficulty, you just don´t have the same public appeal, people don´t just get together in their garages to do Opera, nor it´s something you will find on local pubs and smaller venues.
Because of that, the dude that mumbles Riders on The Storm in exchange for a couple of beers will be very far from the quality he needs to get even a minor role on some Opera, so the bar to get in is indeed a bit higher, but once things get more serious the competition can be even harder on popular styles.
Think for example someone on a corporate band, where you have to do multiple styles and shows can be ridiculously long. Or Heavy Metal where plenty of songs would make Ah! Mes Amis melody seem kinda low in comparision. Or a session singer, when you just have to show up and deliver sometimes without even the opportunity to prepare.
Music Theatre has auditions all the same, the difference is, you will be competing also with the kid that has been performing professionally since age 5 and can go from Opera to Rock and all the variations people WILL ASK for on those pieces, without breaking a sweat, lol.
In short, everything will be hard once you get serious about it. And everything is rather easy when limited to karaoke at home 😛