> I wonder if that principle applies here or not
It applies, but also in practice the maximum temperature is lower than the theoretical upper bound.
I'm confident that the physics is correct, but I hate when things are translated for the lay public:
> "In general, there's no way to "overlay" light beams on each other, because the whole system has to be reversible".
Behold, my two torches.
Oh funny, my intuition when I was writing that was “there’s probably an xkcd what if about this”, but I imagined it be about surrounding the sun with mirrors. Same idea though in the end