In my experience (rather limited, I know), high level adventurers are an army unto themselves. Dominion rules and followers came about for that very reason - the PCs go off to do their thing individually, and only join back up together to face the final threat.
However, if the DM doesn’t want to devolve the game into running a bunch of solo adventures, there needs either some way to handle having each party member doing their part in one location while another party member does their part somewhere else. An example would be something akin to Endgame, where the heroes were split up on different tasks to get different stones, only meeting back up together for the final battle. You could do 5-minute vingenettes for each player, but if done poorly you could see players quickly tuning out when it isn’t “their turn”.
This is where followers can come in handy, allowing one player to run the heavy hitter PC, and the rest of the group runs the various followers. You can rotate between the prime PCs, giving everyone a chance to use their prime abilities and show off what sort of big damn hero they’ve become.