From MY persective, it is the layperson, not the scientist who "hijacked" the word evolution due to the laypersons concept of evolution leading to more advanced things.
In Darwins original thoughts, evolution was simply change that was a combination of mutations and natural selection that allowed things to survive. (edited to add) Actually, in Origins of a Species, the term evolution is not used as far as I can tell, only the word "evolve" and its use seems to match the use of the word for "roll out".
"Thus, from the war of nature, from famine and death, the most exalted object which we are capable of conceiving, namely, the production of the higher animals, directly follows. There is grandeur in this view of life, with its several powers, having been originally breathed into a few forms or into one; and that, whilst this planet has gone cycling on according to the fixed law of gravity, from so simple a beginning endless forms most beautiful and most wonderful have been, and are being, evolved."
There is no link here with evolution being defined as getting better, only that the more survivable forms evolved (rolled out) of the processes that Darwin was studying.
There is no "better" or "worse" in terms of differences between species, there is only "survive" or "extict".
The layerpersons understanding of the word evolution may have caused them to use the term incorrectly, and then it became common to do this. In the end, scientists have always used the word to mean change over time, which would seem to match the current defined meanings of the word and their historical base.