Well, there are some use-cases where Julia is actually faster than compiled code due to being able to compile dynamically generated code on the fly (see https://discourse.julialang.org/t/julia-vs-fortran-complaint...)

But yes, in general the same lack of static guarantees that makes dynamic languages slow also makes code in dynamic languages hard to maintain. I think a lot of programmers tinker with code in dynamic languages and end up liking them as a result, but don't realize the difficulty of working in such a language in a much more complex codebase.