Communication would've happened, but probably between far less actors. So, you have a communication channel which is orders of magnitude slower, and bigger communication needs. Not good.
That said, about the reliability point, I agree with you. If you're building an specialized system, and reliability is your main concern, microkernels+multiservers are the way to go (or, perhaps, virtualization with hardware extensions, but this is a pretty new technology for some industries).
Probably you're going to need to add orthogonal persistence to the mix, to be able to properly recover from a server failure, or an alternative way to sync states, which will also have an impact on performance. But again, you're gaining reliability in exchange.
The communication channel does get slower. The good news is that applications are often I/O bound: lots of comms can happen between such activity if designed for that. One trick used in the 90's was to modify a processor to greatly reduce both context switching and message passing overhead. A similar thing could be done today.
Of course, if one can modify a CPU, I'd modify it to eliminate the need for message-passing microkernels. :)
That said, about the reliability point, I agree with you. If you're building an specialized system, and reliability is your main concern, microkernels+multiservers are the way to go (or, perhaps, virtualization with hardware extensions, but this is a pretty new technology for some industries).
Probably you're going to need to add orthogonal persistence to the mix, to be able to properly recover from a server failure, or an alternative way to sync states, which will also have an impact on performance. But again, you're gaining reliability in exchange.