Nature Structures

Charm, unfortunately, is still not very useful. Even if you're lucky enough to get Titans and Dragons, which is unlikely. It also requires leveling up, just like Summoning. So, what's the point? You still have to level up either one or the other... Again, I repeat about the morale problem, which can be spoiled by the dark factions (Chaos, Death, and Strength, I think). So, Charm can even be harmful, sometimes. Or rather, it's just useless (compared to Summoning). The only plus is that the enemy ranks are thinned out a bit.

Firstly, it's not necessary to take "charmed" creatures into your army; before Equilibris, they appeared nearby even if they weren't taken into the army itself.
Secondly, the example with Titans and Dragons is an extreme case; Charm is much more effective at the beginning, when you have your unit standing on one, or even two, resource nodes. And if you have Half-Elves... it's a fairy tale.
Thirdly, since you don't necessarily have to max out Charm at the beginning, I repeat that 1-2 levels are enough.
Regarding Summoning: first, Summoning is completely useless at the beginning; the summoners just clutter up the slots and reduce the already small number of summoned creatures (if there are many slots, they will summon all units of that level in turn). As a result, in one week, you can summon about 7 Fairies and Wolves, maybe a little more, but usually less, while with Charm, you can gather that many squads in one day...
P.S. To avoid blatant off-topic comments at the end, I'll add that, no matter which branch of Nature you follow, Summoning will not be useful either at the beginning or at the end of development; only at the intermediate stage does Summoning make sense; you can replenish squads of Tigers or Elves.
But Tigers are still better:D Speed and strength are more important than weak ranged attacks:D