Jumps/calls are actually be pretty cheap with modern branch predictors. Even indirect calls through vtables, which is the opposite of most programmers intuition.

And if the devirtualisation leads to inlining, that results in code bloat which can lower performance though more instruction cache misses, which are not cheap.

Inlining is actually pretty evil. It almost always speeds things up for microbenchmarks, as such benchmarks easily fit in icache. So programmers and modern compilers often go out of their way to do more inlining. But when you apply too much inlining to a whole program, things start to slow down.

But it's not like inlining is universally bad in larger program, inlining can enable further optimisations, mostly because it allows constant propagation to travel across function boundaries.

Basically, compilers need better heuristics about when they should be inlining. If it's just saving the overhead of a lightweight call, then they shouldn't be inlining.