the framework Construct provides will greatly speed development versus strictly using a programming language. If you need more flexibility you can access the benefits of a written programming language (Python) by developing plug-ins.
you can use python in your games for scripting, which allows you to add functionality not built into construct, like creating complex data structures, or importing directx control, these can be in your cap file alongside your events. the speed of python commands is about equal to those of actions and conditions from what I can tell.
developing plugins is done with c++, and allows you to create new object types (sprite, and xaudio2 are examples of objects), and it also allows you to create behaviors(such as physics, or platform).
It's c++, so the sky's the limit, and of course it runs very fast.
that's not to say that construct events are slow, or that you need python to make even a complex game. See anything made by quazi for proof that scripting is not needed to make something very custom tailored to your own needs that runs fast with only events.