You can’t–or, at least, I can’t. The other Founding Fathers remain influential today largely because of what they said, but Washington is still significant because everything that he did mattered. While he made plenty of tactical mistakes, most notably in the New York and Philadelphia campaigns, he won enough battles to keep the army together even in the worst of times. He could easily have used his prestige to turn himself into a dictator and his country into a banana republic, but he didn’t. He played an important role in the Constitutional Convention. He hired Hamilton as his Secretary of the Treasury and supported him against his opponents. He wisely avoided war with Great Britain and France. He was an important symbol of national unity at a time of intense factional strife. Finally, he set a precedent by giving up power voluntarily and peacefully after two terms.
Was anyone else available who could have done all of this? Absolutely not, and his contemporaries (even the Republicans) knew it. You can, therefore, easily make the case that of all of the Founding Fathers, Washington was the most indispensable. Our debt of gratitude to him is immeasurable.