Problem 1: Assuming that conceptual systems such as "pragmatism" exist anywhere beyond their places as constructs of cognition convenience in the mind
There is no such thing as pragmatism beyond the meme; it's just a summation word used to define a number of philosophical tenets, and has no innate physical basis. Therefore, it could be stated that pragmatism -- or any ism, for that matter -- is similar to, for example, government-imposed age requirements in that both are artificially constructed for convenience, but neither can be directly deduced by the physical properties of the universe. Put simply, there is nothing preventing us from inventing a new ism similar in scope and definition to pragmatism, but with one additional or one less tenet; ultimately, it's just a word, while its individual constituents are what we should instead be discussing. Even if "pragmatism" weren't useful, again, it's just a word for a handful of concepts, so if any one of those concepts were independently functional, it would be ideal to implement it, regardless of the flaws inherent in "pragmatism" itself.
Problem 2: Assuming that pragmatism has no use
It sounds like your professor is confusing the utility of pragmatism with the lack of useful ideas in his life. Just because you're incapable of inventing ideas of practical merit doesn't mean that the ideal itself is impractical; everything around us has been implemented as a result of its practical value. "I don't see any use in thinking up useful ideas" is a non-sequitur, and even contradictory, as you've pointed out. More likely, the intended meaning was, "I don't see any use in any of MY ideas, so looking for useful ideas must not be useful." Is this more accurate interpretation any more logical? No. In fact, it's so stupid that it actually succeeds in reducing philosophy to its semantics component, all for the glory of some adorable platitude and a bit of ego sex. Tell him to grow up!