Courtney Lee is an upgrade over Tony Allen.
To me, even with respect to their offensive roles, the difference between Courtney Lee's offense and TA's far outweighs the defensive difference.
Courtney Lee is a very good, and very active defender. He is not as good as Tony Allen. For my money, Tony Allen is the best defensive two guard in the league.
But TA limits what you can do offensively. He's trick or treat on the fast break, in a limited role he still averages two turnovers a game, and despite a team that commits itself to the post, TA is such a poor shooter from distance that he only bothered to attempt 7 3's in 13 games (hitting 1).
And while their can be an argument to him slashing, I think anyone who watched the Grizz in the playoffs saw what I saw: TA consistently turn down open looks from 3 because his range doesn't exceed 15 feet.
Meanwhile, slashing is a big part of Courtney Lee's game AND he can shoot at a good rate from 3: Shooting over .400% 2 out of the 3 years he's been in the league.
With the improved perimeter offense in Parker & Gay, I think the ability to consistently hit down open looks is a great asset to us.