A mature audio middleware solution is almost guaranteed to be more feature-rich than a game engine’s built-in audio system; FMOD Studio definitely has features that Unreal does not. Of course, whether you actually need any of those extra features, and which of those features you need, depends on what your game’s requirements are.
You mention you’re building car engines. That’s definitely something that FMOD Studio supports; Numerous well-known racing franchises use FMOD Studio specifically because we make it easy to develop the kind of parameter-driven engine behaviour you describe. We also have a number of features, effects, and plugins that make it easy to customise and tweak those engines in a variety of ways.
You also mentioned time-stretching, cutoff filters, peak metering and visual mixing. FMOD Studio features time-stretching with or without pitch change; multiple cutoff filters that can be driven via automation, various modulators, or both; a visual mixer; and a profiler that can record play sessions in your game and audition them with changes to your mix and game content so that you can audition mix changes in the context of the recorded play session.
If you need help with or information about any of these features, please don’t hesitate to ask us further questions. Are there any other features you want or need?