Not discriminatory in any way shape or form. If you believe it's discriminatory then you need to look at other visas which have requirements others do not. Case in point is the OA visa or extension of stay which requires a retiree to maintain health Insurance with a company from inside thailand, on a HI list, and show this proof annually, whereas a person on an O visa or extension of stay does not have to show this requirement. Many different classes of Visas and many different requirements such as showing 400k in the bank vs. 800k in the bank.
My view with people who yell discrimination is that they have an axe to grind because they don't qualify to obtain said visa.
The tax Exemption was a selling point for me as well as all the other add on, such as only reporting once a year, multi re-entry permit and not having to renew for 5 years to show I still qualified.