I've no problem with summoning being weaker than taming. But how much weaker? Certainly not drastically so. I can even see a decent amount weaker, as to get ancient demons requires a quick casting. But drastically weaker? That seems absurd to me.
As far as I can tell summoners AREN'T drastically weaker than tamers. I see them holding down the spot I farm on my tamer just fine and they're definitely way more versatile. Since we're so set on the "required skills" let's do a little comparison:
2 characters, one has JUST taming/lore/vet one has JUST magery/med/ss - which do you choose? IMHO the answer is obvious; the mage.
The mage can just do so much more. Heal/cure, recall, gate, res, invis, bless, reactive armor, magic reflect, create food, etc. It can even dish out more DPS without eval if its called for. So with all of that extra stuff the base skills of a summer can do, why should the DPS/tankability of the deamons match a tamer who can't do anything besides all kill/heal his pets?
But then again, I'm just a whiny tamer. *sigh*