I agree with you, although it comes out unnecessarily rude.
However, JIT does not necessarily mean fast compilation (e.g. Linear Scan). A JIT might identify hot spots in the code and the optimize the hell out of that part with the same optimizations that GCC -O3 uses. Plus, it might have additional runtime information. Advanced JIT engines usually have multiple stages of optimization.
Its a good point about jit time. It is however also true that even if you do it in the background (as for example Azul does, I think) you are not completly free of its problems. It is often hard to firgure out if it is worth the coordination of the background work. Im not complety sure but I think V8 does advanced optimisation on thread.
Also I am sure that Lua Jit does everything on a single thread. LuaJit is a special case most of the time since it works so fundamentally diffrent almost all other high performace jits in the wild. It only has one compiler and still works with a interpreter.
However, JIT does not necessarily mean fast compilation (e.g. Linear Scan). A JIT might identify hot spots in the code and the optimize the hell out of that part with the same optimizations that GCC -O3 uses. Plus, it might have additional runtime information. Advanced JIT engines usually have multiple stages of optimization.