[Edi]

A weak air bless varies from 20% to 40% in effect, depending on how much air you actually have. If you have shieldless sacred units, even 20% and 30% air bless will have a marked effect on how badly they get mauled by archers, but if you're going for some otehr magic as the main bless, you are likely not going to be able to get A9, in which case the weak blessing is useful. Doesn't cost too much, still offers a benefit and you have points for something else (scales, dominion, whatever).

But as stated, this thread is for discussing the merits or lack thereof of what is included in the FAQ. If that particular section gets a lot of more experienced people's hackles up, it can be removed.