I’m sorry, but “evolution” as a concept doesn’t require increasing complexity. That’s precisely what I attempted to illustrate earlier. And, in my experience, “evolution” is quite commonly used as a term to describe language change.
I just did a google search on “language evolution” and found a long list of sites most of which appeared to be examples of linguists, talking to other linguists, referring to languages as evolving. I didn’t find any indication that these linguists saw themselves as being particularly radical or different from the norm for linguistics.
I’ll have to retract that. Most of those sites are talking about the origin of language, rather than an ongoing evolution of language.
I still have my memories of taking linguistics classes in college and learning that languages “evolve,” and of reading books by linguists (admittedly “popularizations”) which talked about languages “evolving.” But you can not share my memories so I’ll have to go look for something else…