To be honest, there's no much mystery as people say about the human formation. I will not point out everything you said on the commentaries because it's too much (like countering spiders with mana barrier). Centurions was good before, and it was kinda of a must to research if you was ahead on your server, but not because they was good by themselves, but because they was the first gold unit you could get and having a castle lvl 13 with gold units would give a big edge to humans on the early rush. That being said, now that we have centurion, templar, legionnaire, gold archers, priests or even royal hammer all on lvl 4 of academy, there's no good reason to research centurions, simply because they're not as good as ANY other option. As people said above and I don't think there's a need to explain, it's a must to have priests and templars or priests and legionnaires. Centurions counter big units, but they're also countered by big units and will be melted by anything but catapults, swordsman and silver mechs. Even if we had a heroe to boost centurions, they would still not as good as anything else you may choose for you gold cap.
Now, talking about the heroes and your choices, I would like to say that: 1) it's not a must for humans to have natural leader, for other races it can be but not for humans, unless you're using the formation (or a similar one) that Aluminara showed, or don't have extra heroe and sacrificed some archers. 2) you don't need Heal (and for consequence you don't need boosted healing) on Vega simply because it will mess with your rotation, and unless you spent some good amount of ability points on her, it's way better to focus on Favor, some HP for your priests and some points on mana barrier if you're used to use it. 3) talking about Elena, why exactly magic resistance is good against lich? It's as good as against any other race. Scorps and spiders don't deal magic damage and that's pretty much the only thing you will see against a lich that played more than 1 week.
I can't agree with almost anything said on your guide.