It is a bit more complex than that. Tax related things always are - especially cross border. It is true, that foreign income will be taxable. It is also true that the max possible tax rate will be at 35%. However, only money actually transferred into Thailand will be taxable. Also, it depends on many more factors, like tax treaties between the two countries. For many cases, income already taxed in one country won’t be taxed again in another country. But yes: a detailed analysis is advisable before moving.
And I don’t have any questions for you. I suggest you brush up your knowledge about the new DTV visa first. I shared extensive information on it over the past days here - including its original law text.
The actual visa fees for an initial ED visa might be cheaper, yes. But an ED visa has to be extended at immigration every 3 months at an additional fee of 1,900 THB. On top of that, most schools charge much more for their courses, if you require an ED visa vs. if you just book their courses without their support in obtaining an ED visa. An ED visa also has a shorter total maximum length. And no, the DTV is not only designed for remote working - that is only one of its two categories. The other DTV category is explicitly participating in recreational courses and activities.
Nobody knows yet what proof / documents are required to demonstrate eligibility for the DTV in the "Soft Power Thailand" category. But a recreational activity like boxing gym will likely qualify. That would be a good thing - cause the bureaucratic process of obtaining an ED visa and the overcharging often done for that "service" will find an end.
From what it seems, the DTV can be an alternative to Non ED visa in case of non formal education now - likely even make Non ED visa the less desirable option.