SSPL is definitely not open source, it violates #6:

https://opensource.org/definition-annotated#6

That's the point of open source, and free software in a way as well. Copyleft licenses have restrictions, but as long as you follow those restrictions, you can build whatever you want using the software. SSPL, FSL, BUSL licenses outright prevent you from competing in certain commercial ways, no matter what.

Just because most business models don't want to comply with copyleft doesn't mean it's not open source - it just means it doesn't fit your business model.