Scaling and multiboxing

Does the mechanics of scaling ruin high end dungeons that use to require a group? Is it now better to solo them? I use to enjoy needing a group to do freezes and what not to complete a hard dungeon….is there a sweet spot like 2 acts or 3 for end game? Is 5 and 6 no longer viable? If it’s better to go solo do you need a cookie cutter AIEW to be viable?

Nearly all ways to play the game are viable.

It's a matter of clear speed.

It seems like the sweet spot maybe 4 to 6 accounts.