I believe this is Christopher Anvil's "Pandora's Planet" (1956). Humanoid aliens from Central invade Earth to add it to their empire. The thing is that other than spaceflight (and its ability to bombard Earth's defenders) they aren't actually more technically advanced (though they really don't want to admit it).
A human suggests a bayonet to one of the aliens:
"Listen," said one of the natives conversationally, as he was hustled out of the room, "if you'd just put holes in the guards of those knives, you could slip them over the gun barrels, and it would make it twice as easy—" His voice faded away in the corridor.
The aliens consider themselves to be the apex of peoples, regardless of how intelligent humanity is (hat tip to CL) and handwave away any apparent threat to their position as superior:
This unpleasant conclusion led to one that was really ugly, namely, of two races having humanlike characteristics, which race is human, the smart race or the dull race?
At this point in the argument, an unpleasant little man in the back of the room rose up and announced that on the basis of an extension of standard comparative physique types from the humanoid to the human, the lop-tails were more advanced than the Centrans.
But that was the low point in the argument. Soon the hypothesis of "pseudo-intelligence" was introduced to explain the lop-tails accomplishments. Next, a previously undistinguished staff-member introduced the homely simile of passing over the brow of a hill. If, he said, one went far enough in one direction, he at last came to the very top of the hill. Any further motion in that direction carried one down the slope. True, he said, these lop-tails might go further in certain physical characteristics than the Centrans themselves. But to what point? The Centrans were at the peak, and any ostentatious exaggeration of Centran traits was merely ridiculous.
The problem with humans (that makes them "inferior" to Centrans) is that humans have too many ideas:
"You know the principle of the nuclear engines. There is a substance Q that flings out little particles. These little particles strike other atoms of Q which fling out more particles. There is also a substance L .which absorbs these particles. Success depends on the correct proportioning of Q and L. There must not be too much L or the particles are absorbed before things can get started. There must not be too much Q or the particles build up so fast that suddenly the whole thing flies apart.
"Now, consider these natives. What are they like? An engine with too much Q, is it not? And what are we like? To speak frankly, Horsip, we have a little too much L, don’t you think?”
Horsip nodded reluctantly, then said, "I think I see your point all right, but what are the flying particles in this comparison?”
Argit laughed. "Ideas. From what you tell me of these people, they fairly flood each other with ideas.
You can read the story in its original publication, Astounding, September 1956 at the Internet Archive.
