The page summarises the license as “Basically… the MIT do-whatever-you-want license”. The MIT license is of course one of the most popular permissive open source licenses.

This is an incredibly misleading comparison. The subsequent clause is a complete contradiction, not a subtle clarification.

People who use it claim it's Open Source

They are using “open source” as a generic descriptor, not as the unregistered trademark of the OSI.

Yes, and that is the problem. That "descriptor" is not correct. The correct descriptor is "source available".

The descriptor is correct. The source is available to you, free of charge, and you can do anything with it as long as you extend the same rights to your users.

Yes, I agree that "source available" is an accurate description. Unlike "Open Source" licenses, which have no restrictions, "O'saasy" does not allow you to do "anything" you want. Adding a clause like "but you can't compete with us" makes it incompatible with OSS licenses.

I am fine with licensing your code as you wish, but I will always oppose attempts to redefine the widely understood and established meaning of "open source" that has been in place for over 30 years. You don't get to change its definition.

The “established” meaning has in fact been deliberately created by megacarporations like Microsoft so they can exploit free labor by volunteers to make money without lifting a finger. Look at who is sponsoring the OSI.

Ever heard of the Free Software Foundation? Richard Stallman? They are pioneers of free software I'm talking about.

Please don't embarrass yourself with your conspiracy theory nonsense. Besides that, Microsoft contributed to Open Source more than any other company.