You might also give them a highly cursed magic item (oh wait nearly all the artifacts have some bad side effects) You might also attack the stronghold when they are away, make it difficult to find trainers, require training on any new skill, make training cost more money in addition to the xp, Make the training come at a price, part of their soul or something that limits how much of their sanity they can leverage.
I gave a fighter a sweet sword. He had a d10 artifact die, and it had cool effects when it hit. The drawback is that it started to storm each time he pulled it out. Not just a small rain storm but a lightening crashing, high wind, driving rain storm. Any successes from the artifact die were delivered as lightening, but also caused a random roll on the horror table that affected him any anyone within 20 feet. Delusions, nightmares, and paranoia were handed out and caused a huge issue. He still used the sword because it had many benefits, but less often and the party became wary of him. There was also the 'my precious' curse on another item the group had, which lead to a lot of odd directions.
I guess this doesn't really relate to increasing talent issues, but there are some things that talents can't overcome very easily, or that just because you have a talent doesn't guarantee success.