I completely agree. I would only add that there have also been arguments about whether GPLv2 is discriminatory, though they also feel long behind us now.
There is always a case in which all license will be discriminatory when it comes to "specific fields of endeavor". If the endeavor is to break copyright then a copyright license can't permit that. To take a example, permissive licenses do not allow someone to take full ownership of the copyright of someone else work.
As such the Open Source Definition with the phrase "specific field of endeavor" is limited to cover areas which don't involve copyright law. For many reasons, including copyright law itself, it can not grant that which would be the most broad definition of nondiscrimination.
There have been arguments about whether the AGPL is discriminatory, and those have been mostly waved away (wrongly, i think, but c'est la vie).
In that vein, SSPL is arguably a free license. It simply changes when obligations to distribute source occur.
Compare to the the commons clause, which is not a free license - it says you have no right to sell the software as a service at all.