To take the fact that it looks as though they only fly in short bursts of speed and use PIS anti-feats as a justification for the idea's validity is improper procedure. Every time a Dragon Ball Character had to fly any long distance, their speed was shortened for the sake of plot tension and plot tension alone. The same reason why normal humans like Mr. Satan can see them fight. If you want to substantiate the IRRELEVANT claim that DB characters are only FTL in short bursts, you're going to need more than PIS for that. Especially when the way they "teleport" everywhere is commonplace in the portrayal of speed in fiction.
Though they come from Super, numerous examples of characters blitzing longer distances then simply 30ft in a short burst. Goku blitzing Jiren in that iconic MUI transformation is the prime example.
Hell, characters fly while fighting simultaneously in Dragon Ball all the time, often appearing as blurred lines on screen that slam against each other and create shockwaves— for what is implied to be an entire fight, so to say the absence of characters not bogged down by bad writing means that they CANNOT use that speed for sustained distances is bullshit.
Gohan even had to be taught to see their movements by Piccolo, and even while looking, for the brief instants of him getting used to it, it looked like orange and green streaks were slapping against each other.
You can't say "oh, those examples of long distance high speed travel come from DBS, so that means none of the arcs before allowed it to be possible", because you're using the lack of good portrayal to make a claim that's unsubstantiated in your favor.
Just because Goku had never ran across the planet in a sustained race or something isn't proof of his inability to do so, nor is it proof of him having stamina issues sustaining that speed. It's headcanon used to explain bad writing when we need no further explanation for the bad writing than to acknowledge it for what it is. You can't say "Goku could only use a spoon when eating, and he only just learned how to use a fork when he met Chi-Chi," without proof of Goku not knowing how to use a fork before Chi-Chi.
It's also not really rational to call "short burst" running/flight speed (because it's both, all of the Tournament of power is that demonstration) combat speed only, since flying from point A to B, however short the distance, is still traveling, and most Sprints are short bursts of top speed running. If they get tired from flying forever is irrelevant to how fast they can get while traveling.
