GTA VI is, according to reports, set to be 10x more expensive to have been made than GTA V, which at the time was the most expensive video game ever made.Taking the £8.6bn gross for GTAV in his tweet at face value, if they paid $7500 to 3 song writers for 400 songs, that works out to $9milion, or just over 0.1% of the money they make from the game.
Presumably they intend to blow the other 99.9% on hookers and cocaine and incredibly detailed car exhaust animations.
Personally, I don't understand why the original artist would expect a share of the profits when their song is going to feature on one of the multiple radio stations in game, with likely 200+ other licensed songs. And to add to that, the offered £22.5k isn't bad at all - the top voice actors for the game are likely to pocket something in the region of $200,000+ for their voice and there'll be an astounding number of hours recorded. Red Dead Redemption 2 had over 500,000 lines of dialogue and used 700 voice actors. GTA VI will be considerably more detailed.
All in all, fair play to the guy for not just taking the money if he isn't happy with the terms but ultimately, it's not a bad price for what would have been an incredibly minor part of the game.