Yes, although I do think people get too carried away with listing off informal fallacies. Any failure of reasoning that an informal fallacy describes can trivially be shown to be a flaw in the argument without using the label. And sometimes the labels can apply to good arguments (circular reason is a good tool if you want to draw out unobvious implications of a premise, for example).
By the time a philosophy student can use the informal fallacies in a nuanced enough way to be useful (as opposed to listing them off, as you see sometimes in internet arguments as a cheap way to score points), then they can pick apart the flaws in arguments without needing to reference the informal fallacies at all.
To bring this back to the question; we can spend some effort trying to find an establish informal fallacy that "fits" your case; appeal to false authority probably fits best in terms of established fallacies (https://en.wikipedia.org/wiki/Argument_from_authority#False_authority particularly if it's name dropping obscure concepts without explaining them, and trading in on the hope that the reader doesn't check what they mean.
But in the case you describe, just calling the argument an "appeal to false authority" is a much weaker response then digging through it to show that there isn't a successful argument behind the big words. Either "new keynsianism shows that X" is true or false; if it's true, then the arguer is perhaps guilty of a needless lack of clarity. If it's false, then there is a much deeper argument you can make; namely that X doesn't follow from New Keynsianism. That objections makes the informal fallacy at play comparatively unemportant.
By just labelling it a fallacy, you're now open to the objection, true or not, that you didn't understand the argument. Which might be a fault on the arguer's part, but it undermines your ability to make a solid claim regarding the argument's falsity.