We felt the first tier was fine in 10 overall. Dogs, Elegon and Garalon required some hotfixes. ToT was a little too hard on 10.
It's tough because our stated goal is to make 10 and 25 equal difficulty since they provide same ilevel.
But the majority of 25 guilds are heroic guilds. That means 25s overall tend to be more skilled than 10s.
So even if the difficulty is the same, 10s end up feeling harder to their actual audiences.
Yet nerfing 10s adds to the pressure of having 25s just give up and run 10s since effort per reward is easier.
Tough problem to solve, which is why I sometimes opine if the ICC model of lower ilevel for 10s worked better.