1. Please read the paper before making that judgement; it is brief. The paper is focused on variation of visual representation of concepts, not variation of concepts themselves. That the concepts of “smiley face” or “pizza” are sketched differently by different people does not mean that those different sketches are actually representing different concepts. They very clearly are still representing the same concepts.
2. However, there can absolutely be variation of concepts without necessitating treatment of those variations as separate concepts (up to a point). There are very strong arguments for understanding concepts as being very often not rigid but fluid/cloudy. Football and crossword puzzles are both wildly different variations of the concept of “games” for example, yet that concept is able to contain such disparate variations without becoming absurd or impractical. See Douglas Hofstadter’s books “Surfaces and Essences” and “ Fluid Concepts and Creative Analogies ”; Wittgenstein’s “Philosophical Investigations” also touches on this, as do many other reputable thinkers in philosophy of mind.
2. However, there can absolutely be variation of concepts without necessitating treatment of those variations as separate concepts (up to a point). There are very strong arguments for understanding concepts as being very often not rigid but fluid/cloudy. Football and crossword puzzles are both wildly different variations of the concept of “games” for example, yet that concept is able to contain such disparate variations without becoming absurd or impractical. See Douglas Hofstadter’s books “Surfaces and Essences” and “ Fluid Concepts and Creative Analogies ”; Wittgenstein’s “Philosophical Investigations” also touches on this, as do many other reputable thinkers in philosophy of mind.