Interesting, though speed in diesel world is certainly relative, so I might change "pre-chamber diesels rev faster" to "DI diesels rev even slower", since I owned a Honda 350cc w/ 10,000 rpm redline and have a 1965 Dart w/ 4.5L V-8 and 7000 rpm.

I wouldn't have expected the combustion time to limit the rpm. It is partially controlled by how the injection pump meters the fuel in over the downward piston stroke. DI engine fueling is much different, so compromises there could also explain lower rpm capability, rather than the speed of combustion. Newer diesels have much finer sprays (due to >10,000 psi fuel rail), which speeds droplet combustion and gives more thorough burning.

20 years ago I worked in liquid spray research, which over-lapped with diesel researchers. At that time they were just beginning to learn what went on inside the engine. They were just starting to get photos inside the cylinder and measuring drop sizes. They did find that much of the spray crossed the cylinder and impinged on the far cylinder wall (in big DI engines). Finer sprays helped a lot with that. I don't know how much more they know today (or think they know). In the end, it all comes down to running an actual engine and optimizing it as a black box.

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1984 & 1985 CA 300D's
1964 & 65 Mopar's - Valiant, Dart, Newport
1996 & 2002 Chrysler minivans