Harmony - Troop Symmetry

Nargott, I disagree with you. The idea is still worthwhile, even without implementation (it just needs to be fleshed out).

Considering what percentage of ideas make it to the detailing (project) and implementation stages, and how much time and resources are spent on simply coming up with an idea versus its implementation, their value is close to zero. At the very least, there's no point in considering something that will never be implemented.

the main problem with seraphs, and in general, I think, is just to spark interest in creating them

Well, for starters, try to get yourself so interested that you actually implement it :)
If you search online, you can find thousands of ideas for Heroes, but they're all useless because it's one thing to write something down, and another to implement it (and the chances that someone will work on implementing someone else's idea for free are close to zero, especially when it requires real effort).

As for the seraph, there's no point in blindly copying a religious image, because the power of a seraph in the game is nowhere near what it should be (it's much stronger than an archangel). And the same goes for cherubs.

As for the criticism of the idea itself, it's a matter of taste; at least no advantages of symmetry are mentioned, while the advantages of asymmetry are obvious: diversity.