Unikernels simply redraw abstraction boundaries. You can still use libraries and third-party code to implement common primitives. In fact, that's exactly what many unikernel frameworks give you (unikraft, hermit, mirage)
With a capability-based microkernel you get to assign ownership and resources to a very granular level that increases robustness against crashes and protection against attacks to the core system policy. A unikernel can give all of that but I feel like then it will be worse to program against rather than a microkernel.
So overall I don't see any advantage of unikernels. They don't help you write more correct programs IMO and the performance gains are limited.
IME you can eliminate tons of issues using language-based safety. That just wasn't possible before Rust without taking a perf hit. And you can still use vm in a unikernel for e.g. guard pages, read-only segments, demand paging etc.
I'd say the main advantage of the unikernel approach is the ability to be very intentional about where/how you introduce complexity. For a certain class of high-performance systems software, that has direct implications on reliability and performance.