Of course heroes on the battlefield could be done in such a way that it would work, and it would be very enjoyable and add a great deal to the game. I am relieved, however, that in H5 the developers did not try to implement something like this, because they have yet to get aquainted with making HoMM games, and if they were to try it right now they would probably result in another disaster like the heroes on the battlefield in H4. It's much more reasonable to first get the basics down, and then attempt to innovate. Given the on-the-verge-of-collapse state of the HoMM franchise, it's perfectly logical. Although I do have to admit that heroes on the battlefield are quite fun.
Oh, and despite Nival's apparent aversion to anything H4-related, we have to keep in mind that many of the features in H5 are actually more similar to Heroes IV than to III. Take the skill tree, for instance. It includes general skills similar to the primary ones in H4, with various abilities associated with them, like the secondary skills. This resembles H4 much more than the array of all-secondary-skills in H3. In short, they are not completely opposed to everything H4, and are willing to implement some of the improvements that game offered. The fact that this doesn't extend to caravans continues to baffle me, though.