No one has developed a full alternative in one package. That's because some of the practices are really bad and shouldn't be solved the way the GP describes they are solved. Data stored in SharePoint, the worst MS tool ever maybe, is one example. O e wouldn't build another SharePoint, because why make something that sucks so much and then store data in it? It is moronic to do that.
And the GP is right in that the more moronic stuff people do, the harder it gets for them to no longer do that and somehow extract all their data into usable and useful form. Microsoft will happily go on making bad products, if that keeps its users prisoners.
No one uses sharepoint because it's good or was ever good, everyone knows it sucks. They use it precisely because it's a) bundled with 365 already and b) already very well integrated into the rest of the entire ecosystem. No developer time is needed to get automations, external sharing with encryption, and any other numerous features.
So sure, one wouldn't build another SharePoint on its own, but there's still room to build an entire package like M365 and do it right, and integrate solutions that don't suck.
But no one does, because it's expensive as hell. Good luck building something just as comprehensive and integrated and selling it for a measly $22/user/month.
Hasn't training been already ruled to be fair use in the recent lawsuits against Meta, Antrhopic? Ruled that works must be legally acquired, yes, but training was fair use.