In any case, we're waiting for a bright, fantasy turn-based game here, not a depressing medieval battle simulator where everything, down to the last feather on the helmet, must conform to logic.
Well, it's already clear that it will be turn-based. As for the "brightness," I'm not so sure. HoMM is valued for its interesting world, and the components of that world must match the whole in quality.
Realism doesn't limit the concept artist's freedom in any way. It just gives him common sense. If a warrior is wearing more armor than he weighs, or if his weapon makes his center of gravity incompatible with the ability to maintain balance, then that's a fail.
I can easily accept the stylish look of the Seraphs because it reminds me of advanced magical technologies. There's an explanation for that. But how do spikes on the back allow the Tormentor to torture its victims?
I would say this is an unprofessional approach. I might expect such a design from browser games, but not from a mainstream title of one of the most famous brands in the world.