We all have preferences. My preference does not impact yours.
it impacts when I am asking for a change to be made as either an optional add on to one class or a new class and you keep yelling "No...if he gets what he wants I wont play"
I think the reaction is not to @Oofta per se. They can have their preferences of course and express them on a random message board, even the extreme "even if they continue to have great chicken, I'll refuse to eat at this restaurant if they start serving great steak".
The negative reaction for me anyway is because they are embodying a position that seems to come from a vocal minority that had outsized influence on the Next playtest and could have influence on further design.
It's just a hunch of course, but I strongly believe that the vast majority of players would not have a stroke and go play something else if an option like the mythic martial class was introduced alongside all the existing options as long as it didn't raise the power, versatility, and narrative ceiling for classes past current casters.
In fact, a lot of people would choose to play it. So maybe that is the fear? Despite people's insistance that the Fighter is fine, perhaps if this class was introduced they fear their fellow players choosing the new class and then their preferred asthetic and playstyle would not be as common? That seems like extreme selfishness as of course the table could just agree not to use the new class if they all collectively wanted to preserve the status quo.
I've seen no mythic martial supporters that have a problem with current Fighter + magic items existing. Some current Fighter supporters have this view that introducing a new self-contained mythic martial class that could be just disallowed at their table would ruin the entire game to the extent that they would play something else. So yeah, that ain't cool.