To hardcore fans of course. And right now he is considered a Top 5 fighter all-time by any measure, BUT, if he gets smashed in his return to the UFC questions about his legacy will increase especially as the UFC grows and gets more mainstream. Fans constantly have to be educated, and this would make it harder on us hardcore fans to continually do this.
So this is more important than you think to Fedor on a broader scale. If he wins the UFC HW belt he will have the opportunity to erase ALL doubters and be UNEQUIVOCALLY known as the best of all time, the absolute GOAT which right now he is interchangeable with Anderson, GSP and Jon Jones.
Very few times in life someone has the chance to be universally known as the best ever; Michael Jordan and Ali are examples. This is Fedor's change to have 99% believe he is the GOAT.