Is there any point in switching to mesh shaders if I don't have any use for the flexibility they provide? For example, do the new semantics allow faster execution on newer hardware for converted boring vertex shaders?
The preformance advantages only come when you can take advantage of the flexibility to apply new optimisations. Such as sharing work across a mesh invocation, or avoiding launching mesh invocations from task/amplification shaders, or avoiding vertex fetch (procedural generation).