The talent tree for a given class is fixed. The available upgrades for each hero would be the same. The degree to which those upgrades help a particular hero is dependent on the specifics of that hero.
For instance: the hero with the highest special damage % will see the biggest lift from +Attack in the tree. So a relatively low attack hero like Marjana may benefit a lot from an extra 75 pts of Attack.
Heros with very high defense and low health will benefit a lot from +Health, since the high defense makes each point of health hard to remove. 180 points of health might make a mediocre hero on defense very good.
The talents themselves play very differently with different heroes. A hero with high defense will benefit a lot more from the Paladin talent than a hero with low defense.