I found with RAF...

I had two accounts more than half full of 70's.
And leveled a ton of characters to 60th.
Then did the account transfers.

WotLK comes out shortly thereafter.
And I race one team to 80th.
And start to really play them.

A while later, I get the urge to level others to 80th.
And bounce back and forth between three or four teams.
Always playing with rested.

60th to 70th, is only 70% of the experience required.
70th to 80th, is only 75% of the experience required.
It is very easy to hit a 5% guild bonus as a boxer with their own guild.
You could easily join a guild with a 10% leveling bonus.
And then there are heirlooms, for 2x 10% leveling bonus.
If you had heirlooms x2, and a 5% guild bonus, that's 2.5 levels free in each 10 level bracket.
So less than half of the 60-70 process required and half of the 70-80 process.
80th to 85th, is rather easy as well.

I agree it is a lot of work to get say five teams to the level cap.
But the one team, that is most magical to play... whether it is for PvP or PvE-Heroics, or achievements...
It isn't that hard to level them up, and when boxing is relatively new it is very fun and a little addictive.

Over the course of 2 years of Catalcym, I'll level all nine teams (7 alliance, 2 horde) as far as I intend to take them.
One per faction intend to reside in the 70-74 "twink" bracket.
The rest would like to be 85th; I've only got two teams at 85th so far.
But with a two year window, it's not that hard of a process.