Does it reduce programmers performance skills by working on thirdparty controls such as devexpress , telrik etc ?

Doing something that many component vendor don't give you very useful skills provide that their components are usable enough...

Required skills depends a lot on the type of appplication you create and the expectation on the product and the culture of the enterprise.

If you want to improve your skill, then WPF or Windows universal application would make more sense than using Winforms. Those technologies lead to better separation of UI and code and this is an important skill if you want to be able to update the UI of the application without rewriting all code or improve the logic behind without redoing the application.

Their are skill like writing sort algorithm that although is nice to do in school, it is almost useless for application coder as they can use existing algorithm written by professionnals.

Why using efficient tools would make you less skilled ?

Efficient tools make you efficient with less pain, it will make less skilled people more efficient, but why would it lower your skills ?

you know riding a bicycle, do you forget if not practising ? Ok it can get time if you don' t practise for long, but do you forget ?