I just read where Russian Su-30 engines are intended to operate 300 hours
before major overhaul. How do US engines compare? 300 hours seems awfully
short to a layperson like me.

The whole engine doesn't get overhauled, just modules. Each module, ie fan,
compressor, turnine, fan drive turbine, etc has a different interval, usually
based on cycles, ie temperature excursions from cold to hot.

Fighter engines typically stay installed for 300-600 hours on average and come
off for repair not overhaul.

The Soviets/Russians have always made disposable fighter engines from what I
know. Run'em hot, burn'em up, then salvage/overhaul them. Eliminates most of
the logistics tail and cuts way down on traing requirements. Gues you can do
that when you own the world's supply of titanium ore and most of your troops
are illiterate.