Yes that is true. There are applied sub-disciplines for all of the science. Typically you would call that something like "applied computer science" or "computer engineering", but CS is new enough that it hasn't split like that yet.
Nobody is saying that's not important. But the field as a whole began before mechanical computers were invented or practical, and there are several subfields that are basically indistinguishable from mathematics.
I mean, if you want to relegate CS to only mean theoretical CS, then you’d be in a small population: most theorists don’t want that, even. One of the cool things about CS is the rich interplay between applications and theory, and separating the two would only harm both.
Nobody is trying to relegate CS to a theoretical discipline. But theoretical CS exists, so it doesn't make sense to claim CS is the study of mechanical computers. Since it started as a theoretical discipline, it makes even less sense to say that the field was founded when we first figured out how to practically mechanize the ideas in CS.
I mean, my university still has separate Chemistry and Astronomy departments, but at yours following your preferred nomenclature, how do they distinguish among all the resulting departments called stuff like "Applied Philosophy", "Applied Philosophy" and "Applied Philosophy" ? Or is it that for some reason you think only Computer Science should be singled out in this way?
But Chemistry cares about actual chemicals and Astronomy cares about our actual universe. Likewise, Computer Science is overwhelmingly concerned with actual computation. You aren't identifying a distinction here.
Both Software Engineering and Computer Engineering exist, as sub-disciplines, but it doesn't make sense to argue that somehow studying Graphene (a chemical which exists) is Chemistry while studying non-blocking algorithms is only Applied Computer Science somehow just because such algorithms could be used on an actual computer.
Nobody is saying that's not important. But the field as a whole began before mechanical computers were invented or practical, and there are several subfields that are basically indistinguishable from mathematics.