No effin casual will play a season for 3 months. Even die hard diablo players(streamers also) check out before the end if the season isn’t good. “Season is 3 months long, just progress gradually” is the biggest delusion and cope I’ve heard from someone.
End game is probably T70+
Being able to delete Uber bosses within seconds and having them on the farm rotation is the beginning of the end game.
End game is having decked out gear with 12/12 perfect masterworks.
If you are a guy with non GA uniques and no ubers and you are doing T60, you are as far as you can be from the end game.