With your suggestion, it could easily lead to "hero-digging" in Heroes 4. Have you played Heroes 3? Do you know how they dig around in the tavern until they find the right hero with the right specialization?

Moreover, you can only buy one hero per week. You'll have to dig around even more. And in online play, it could be a decisive factor.

Well... why can you only hire heroes once a week? Correct, because in the tavern, you choose the one you need with the skills you need.

This is already somewhat unfair. Skills should be earned through effort.

Well, in 3 and 5, additional skills are also given "unfairly," but it doesn't hinder the game.
Let's say you can choose a hero who is different from others because of a more appealing appearance, and you can mold him into whatever you want. But isn't it more enjoyable to find a hero that you like, one that matches your favorite tactics and skills? IMHO, it's definitely more interesting. And you immediately develop a fondness for a particular face, you distinguish it (or him) from the crowd, and the game becomes more enjoyable, IMHO.
By the way, I haven't had to use the "hero-digging" method because I choose the right hero at the beginning, and one is usually enough for me. :)
Well, that was just my opinion, I decided to share it; I would like it if it were implemented. :)