Lead core/jacket separation does happen at higher velocities. But it still kills quickly when the bullet is put where it needs to go.
Even bonded bullets can separate.
Solid copper bullets can not expand
Jacketed bullets can not expand
Copper bullets can deform and change course
Jacketed bullets can deform and change course
Every bullet type can and has failed
I have used high velocity jacketed lead bullets from 3650 to 2800ish fps MV with great results on deer and elk, and one antelope. From 18 to 1000+ on big game. And from 6 to 1365 on coyotes. My PERSONAL experience is good enough that I keep using them in all of my rifles except when hunting a particular area that requests the use of non-lead ammo.
Do you hear about VLDs and other jacketed lead bullets not performing? Yes. Because probably 80% of hunters USE jacketed lead bullets. The ones I usually discount are the guys that claim it was a good hit but the bullet never expanded or blew up, but the game was never recovered. Easy to say you made a great shot but the bullet failed when you have no evidence with a dead animal to prove your case. Strange things can happen to an animal when hit, and some of them are tougher than a $2 steak. Even a 100% fatal perfect double lung & heart shot can end with an unrecovered animal. So can a brisket shot or the unheard of "miss".