no, the visa is not for living all year around in Thailand, but the rules make this possible by only leaving short time. (minutes).
If they wanted to create a visa where you can stay whole year around they would have given it a stay of 1 year with possibility to extend for 1 year in country for the full 5 year.
So DTV now is legally used in a way they did not want when they created the visa.
You use the visa completely according rules, but not the way they meant it when it was designed.
The fact that a normal stay is up to 180 days and only once can be extended is a sign that the targeted a group that normally will not stay over 180 days and then go for months to an other country live there too as a digital nomad and then maybe again return for some months. That is what digital nomads generally do.
A lot of remote workers also cannot work full year around at the same place, it has a reason they use "workcation" for this.
You and a lot of others belong to a group that was not the target group for this visa and that might be the reason immigration makes you feel unwelcome., even when you completely following the rules.
I think they assume that somebody who applies for a visa for over half a year to live in another country doing Muay Thai training at least should have some previous experience.
They just want to check if your application is genuine.
My reaction is about you calling people in this group rude, obviously you read it and don't understand it, I will remove it because it is not informational for anyone else than you.