The -2 is a significant bonus for the squishy's defence and the damage from not attacking the paladin is significant.
You have to attack or be adjacent in order to maintain a mark.
I'm more cncerned about an Archer-Paladin once people can create their own characters. "I shot you from way over here and move away. You're now marked and you can't reach me so you're taking more damage and you have a penalty to hit my pals if you can reach them."
Marks are not supposed to be a perfect defence for everyone else; just to help defend them. Of course in 4E the PCs seem to be outnumbered a lot anyway.
You have to attack or be adjacent in order to maintain a mark.
I'm more cncerned about an Archer-Paladin once people can create their own characters. "I shot you from way over here and move away. You're now marked and you can't reach me so you're taking more damage and you have a penalty to hit my pals if you can reach them."
Marks are not supposed to be a perfect defence for everyone else; just to help defend them. Of course in 4E the PCs seem to be outnumbered a lot anyway.