> with more artists insisting on getting those rights upfront

I doubt that unknown artist can negotiate anything. What you are offered is better than nothing. Big corporations abuse their position all the time, individuals can not realistically opt out. The only option is regulations and law enforcement.

> What can WB or any other major label offer an artist like this in exchange for the gigantic ask that is "we own all your stuff forever and btw we also own any re-recordings of these songs"?

Advertisement, legal protection (mainly from themselves), access to traditional media, and distribution in general. How many artist make it out of the big labels system? There is a reason for that.