Looking at several different isolated converter topologies, flyback looks like it's the simplest at first glance. There's only one switch, so there's only one driver, which (all other things being equal) should reduce the cost. However, at high power levels (5kW+) flyback seems to generally not be considered practical. I asked why early in my career, and the answers I got were vague.
I met one person who was commonly winding his own flyback transformers; he said he got 500W out of one once, but just barely, and with lots of rewinding to optimize the transformer. The commercial manufacturers I talked to went silent, or asked what insane thing I was doing to want a flyback transformer that big.
An old book I came across said that flyback transformers need to be operated at high frequencies, and the available switches couldn't survive the stresses of a flyback converter at those power levels. However, it wasn't clear on why those stresses were worse than other single-switch topologies, like boost converters. Nor was it clear on why the frequencies needed to be so high. I suspect it's because exceptionally tight coupling is needed across the transformer/coupled inductor, which limits the choice of core materials and sizes, dictating frequency choice, further dictating switch selection. But that's just a guess.
So what's the real deal? What's the effective power limit of the flyback topology, and why?