Can you imagine the articles if Roger had said: "Yes, certainly, we are the best ever." The tards and lots of fans would view that as hubris, not a help to RF's sublime public image.
Plus the next question would be, "So you've had the most weeks as Number 1 among the Best Ever Generation, so by logical extension aren't you the Greatest of All Time?" Then there'd be articles about a haughty Fed --- certainly not what the boardrooms of his sponsors want to see.
Besides, most people think he's the GOAT, there is no upside gain for him proclaiming it.
Roger handled the question in the best possible way. He is perfection personified, of course. What did we expect?