You absolutely can have the same power with less capable language (I consider Qt an extended C++). Then why we have inheritance and virtual functions in a lot

You absolutely can have the same power with less capable language (I consider Qt an extended C++). Then why we have inheritance and virtual functions in a lot of languages, even though they can be emulated just fine by function pointers in C? Why we need templates when they are just glorified macros? Why we have lambdas, when it is just a syntax sugar for functor in C++? Why some languages offer pattern matching when it is just a bunch of "if" or "switch" under the hood? Why we need async/await, coroutines and generators, when the same functionality can be implemented with POSIX threading? Because these higher abstractions enable us to write programs with faster speed and less bugs. It is also much easier to reason about program behavior with higher abstractions. So the argument that one can do the same thing in a less capable language without feature X and hence feature X is pointless is a false one. If you resist the usage of higher abstractions, you can write a large complicated program just fine, but you won't know what you are missing, how programming would be much enjoyable had you realized the full potential of abstraction.