Tell that to all the people complaining about dragging a cleric around the battlefield.
Maybe if you play adventures league, but in all my home games people coordinate their characters. If someone wants to play a shadow monk, they will ask the others to take Blind Fighting or Devils Sight.
Dimension Door is on page 233.
I precast at 8th level, for 10d8.
I multiclassed too much to get 9th level.
You can use Scorching Ray and get 9th level. But I prefer EB.
The 2nd PC readied Dimension Door for my turn.
- It's my turn.
- I approach them with 15', in any number of ways. (Readied Dimension Door, Phantom Steed, walking out of a bush with Haste, following the barbarian who rushed).
- I kill them.
- End of my turn, nothing happens because they are dead.
For Vecna.
- It's my turn.
- I approach with 15'.
- I use EB once.
- Reaction teleports 30'.
- I use the extra speed I have from Haste / Phantom Steed to move closer. Longstrider also doesn't require concentration. Maybe some magic boots.
- Action surge, quicken, and haste to kill her.
- End of my turn nothing happens because she is dead.
She could escape Scorching Ray, but not EB.