Brook has changed for those who have said he has no character arc.
Him discovering the SHs after 50 YEARS of being alone, watching his crew die and being trapped as a being unable to die form aging at least seemingly (hes 90 now or so technically) and going crazy from the immense isolation has been and is literally the best thing that could ever happen to him since losing his crew at least.
Brook is much happier, much more successful and now a world renowned musician who sells out tours and is beloved by the world too. He's not alone anymore, he has family/friends and he's not suffering anymore.
When Pedro died, he fucking broke down because he got close with Pedro as a friend, probably feeling some similarities to his former crew or someone he knew as a former convoy guard or whatever before he had his crew or something.
Pedro really went out like a GOAT too, the anime really made this scene better too!:
Brook almost watched him lose another crew and being completely helpless/powerless to stop it at Sabaody. He tried to protect Sanji and Usopp with his own life seemingly as far as he knew.
He also saw what happened with Kuma back at Thriller Bark and was the only witness IIRC, him and Sanji were the ones to discover Zoro covered in blood and such too then.
Brook is an extremely tragic and understated character. This disrepect on him genuinely makes me angry.
Brook is one of the best godamn parts of One Piece. It was fucking disgusting/aborrent that 4Kids had the fucking nerve to replace Laboon with a fucking literal iceberg too!
But anyway thats off my chest now, rant over.