Consider this. You are a div 4/5 player. You admire the people in prem and want to be as good as them.
Now you are a div 2 player, you've been practicing and you think your pretty good. all the old prem players who you used to admire have left the game and the old div 2 players have moved up. in your opinion the skill level in prem has decreased because no one is as good as those old player you used to admire.
You are now prem. A few old players aside, the people you started playing tf2 with are all the prem players. Has the skill level decreased or has your perception of it not changed? You still see yourself as not being as good as the old-school players that you admired and looked up to therefore anyone who is below you is automatically not as good as those players. in your opinion the skill level has decreased.
In actuality we have no way of measuring this because while players have made their return they arent the same as they were back then.
The top team now will never play the top team from 15 season ago. you cannot measure skill level it is all based on perception.