If we are arguing from the common uses of the term 'philosophers' then that isn't the case. Logicians make progress in the same manner as mathematics, and are sill classed as philosophers. (They also have strong links with computer scientists professionally but thats a side point.)
If your definition is that Philosopher = person who does not make "real, mathy progress" then its just a tautology. All members of this set, who don't make progress, will not make progress, become obsolescent and be replaced.
Sorry if I sound confrontational. But I am unsure what the larger point that is being made about the methods/knowledge of philosophers. It seems to primarily be a tribal "computer scientists good, philosophers bad" statement, unless something precise and meaningful is meant by "philosophers."
Yeah, common usage. Things like "Are they on the payroll of the Philosophy Department?", and "Do students study it to avoid getting into hard sciences?". (I acknowledge that the philosophy I was taught covers long-dead white guys, not modern breakthroughs - the sorry state of philosophy classes is only a weak point against philosophy, like the sorry state of science journalism.)
I got the impression that people who actually invent logic (like Boole or Gödel) were either classified as mathematicians in their time, or classified such nowadays even though they called themselves philosophers. (Like we call early physicists physicists, not philosophers.) Counterexample?
Y'all know the rules: