I believe yes. For example Prime Fedor, Prime, Conor, Prime Anderson Silva, etc. Are all a force to be dealt with.
Lets not believe the bullshit rumors that any of these guys were/are INVINCIBLE in their prime. They were
1. On top of the Game
2. Highly confident/ motivated
3. VERY hard to defeat
but..
4. Human and beatable like any fighter can be.
you can see when a fighters confidence, physical ability, knowledge of the game, and expert preparation all peak at about the same time and contribute to a large streak of wins, or holding down a title for a long long time.
As Conor said,about aldo, something along the lines of: ' this game is designed to break you, he was a great champ but he is on his way out, I am on my way in, just beginning'
Hopefully a fighter will recognize when he is on a downswing and quit while ahead of the game