Some of this stuff kind of depresses me.

Frame rate drops - I can live with! The original was rife with that stuff.
Pop-up/Pop-In - Not an issue! It literally happened with every asset in the originals.
BUT! there are a bunch of missing songs from San Andreas and Vice City, some of these are incredibly important to the experience - someone got sick with the cheapness:

Grand Theft Auto: Vice City

Ozzy Osbourne – ‘Bark At The Moon’
Kate Bush – ‘Wow’
Michael Jackson – ‘Billie Jean’
Lionel Richie – ‘Running With The Night’
Herbie Hancock – ‘Rockit’
Afrika Bambaataa + The Soulsonic Force – ‘Looking For the Perfect Beat’
Michael Jackson – ‘Wanna Be Starting Something’
Sigue Sigue Sputnik – ‘Love Missile F1-11’
Gary Numan – ‘Cars’
ABC – ‘Poison Arrow’
Aneka – ‘Japanese Boy’
The Buggles – ‘Video Killed The Radio Star’
Joe Jackson – ‘Steppin’ Out’
The Fixx – ‘One Thing Leads To Another
Quiet Riot – ‘Cum On Feel The Noize’

Grand Theft Auto: San Andreas

Tom Petty – ‘Runnin’ Down A Dream’
Joe Cocker – ‘Woman to Woman’
Fatback Band – Yum Yum (Gimme Some)’
The Gap Band – ‘You Dropped A Bomb On Me’
George Clinton – ‘Loopzilla’
Roy Ayers – ‘Running Away’
Tupac – ‘I Don’t Give a Fuck’
NWA – ‘Express Yourself’
Ozzy Osbourne – ‘Hellraiser’
Rage Against The Machine – ‘Killing In The Name’
Black Harmony – ‘Don’t let It Go To Your Head’
Blood Sisters – ‘Ring My Bell’
Augustus Pablo – ‘King Tubby Meets Rockers Uptown’
Charles Wright – ‘Express Yourself’
The Blackbyrds – ‘Rock Creek Park’
Bobby Byrd – ‘Hot Pants’
Bobby Byrd – ‘I Know You Got Soul’
James Brown – ‘Funky President’
James Brown – ’The Payback’
Lyn Collins – ‘Rock Me Again And Again’
The J.B.’s – ‘Grunt’

So the switch version is missing soundtracks or all the versions?

All the versions, they're all the same.