v8 isolates are still shared kernel

while microvm's are separate kernel + hardware virtualization through hypervisor guarantees

I wouldn't call it bad either, just different tools for different things

Not only are they shared kernel... They're shared process, shared address space, shared memory pool and allocator... In fact, there is very little isolated about them at all.

I bet there are a million ways to cause side channels allowing learning about other code or data on the same machine, and just one V8 bug (of which there have historically been thousands) let's you take over or modify code in another isolate.