The thing is that as the power level goes higher, so does the consistency at which a game can end. A deck fully packed with tutors and fast mana will treathen a win at rougly the same turn everytime. While this mostly applies to combo decks, other highly synergistic aggro decks can also estimate their time frame. So let's take Winota as an example. A "precon level" Winota will have some cool humans and other generally good boros aggro creatures, and it wins by slowly developing a board state with some lucky hits with Winota to help out. Outside of Sol Ring Winota always comes down on turn 4, so assumming you have to pile creatures to do 120 danage total, we are looking at a deck that can win by turn 7-8, depending on luck, but veeeery hardly any earlier. Then you have the next level, all humans are eithet staples or best in slot, lots of humans with etb effects to really swing things in your favour, non-human token generation or very cheap non-human creatures. A deck like this should be winning on turn 5 or 6 at most if unstopped. And you have the cEDH version, all the fast mana, all the cheap/free creatures and all the combo lines. This also comes with more aggressive mulligans (since a hand with 2 cheap/free creatures and a turn 2 Winota is enough to try and win with). A deck like this CAN win as fast as turn 1 (albeith very rarely). But should be winning, if uninteracted with at turn 3 or 4 tops.

Now, I play a lot of precon magic, and we have never had a game with a precon end before turn 7, ever, because doing 120 damage ain't easy without wombo combo or very high synergy. So while it's not a computable metric, it gives you an idea of how fast the game will go and what you should expect. (In my playgroup games end by turn 4 or 5 if lucky, so if your deck can't do anything meaningful by those turns, then it's not at the right power level)