You're right that getting music onto DSPs has been commoditized.
Parent may have been referring to promotional deals (getting onto official Spotify playlists, Discover Weekly, etc) or special royalty rates. The major labels have tons of leverage, and they definitely cut deals that entry-level artists don't have access to.
You highlighted the difference though. Independent doesn't necessarily mean entry-level, and indie artists who do manage to develop large followings on Spotify are absolutely in a position to negotiate better rates. Regardless of recent controversies, the company doesn't actually want to lose any artist from the platform, because there is an actual tipping point when the availability of the total global music catalogue influences consumer purchasing decisions. Spotify took advantage of that tipping point and won the battle when Pandora and others failed to secure large enough catalogs.
Parent may have been referring to promotional deals (getting onto official Spotify playlists, Discover Weekly, etc) or special royalty rates. The major labels have tons of leverage, and they definitely cut deals that entry-level artists don't have access to.