Allowing power leveling is never a good thing to have in an MMO. DDO has a fair system in place to discourage it. As is, without Destinies counting towards your level there is a defacto power-leveling option built in without penalty... putting epic 21-25 on top of that without the traditional restrictions would just compound the issue.
At the end of the day, people will take their 24th and 25th levels for the same reasons they used to take their 19th and 20th. If what's available at 24-25 lacks incentive or content that demands it, then they should incentivize it... not open the whole power-leveling can of worms so that people can further trivialize post 20 advancement.