It’s a VERY widely disparate world. There are bottom-feeders and there are high achievers. In Part 135 especially, profit motives are often a driver towards the bottom, and price competition in busy markets can yield some skinny operations that cut a lot of corners, which includes pilot compensation. Sometimes you get what you pay for. In lean times, they draw qualified candidates who make up for their weak practices. In flush times, when pilot hiring is strong, the experience levels drop precipitously and these operators get markedly less safe.
The best 135 and 91 operators are run to a high standard, and no 121 pilot would feel out of place. The difference is often the variation of airports, from very small to hub, that most airlines don’t see. Some of the airports are more demanding than the usual, and that does up the risks.
In general, the better 91 and 135 operators are very safe, but it’s not always easy to judge from the surface which one is really reliable. In the Kobe case, one of the issues pilots frequently bring up is the lack of an IFR pilot. But... it’s SoCal. IFR currency isn’t just rare; it’s almost nonexistent. The metric of IFR = safe is just hard to apply, because of the operational constraints inherent to the environment.
What isn’t debatable is whether being close to high-profile, high net worth passengers can skew the equation. The best operators do their best to defuse that pressure, but not all are successful. I’ve flown for great operators and passengers who never put that pressure on, but there are others who will turn the screws to get what they want.
The band between great and awful is much wider in the 91/135 world, but there are certainly operators that are every bit as safe as the airlines. It’s the lower hours and the wide variation that skew the trends.