Eidolon experiments

I've been toying around with 20th level builds for no particular reason.  After giving up on understanding why the Magus spell list is populated with polymorph spells that prevent spellcasting and armor bonuses, I shifted to the Summoner, since the Eidolon point-buy system makes for interesting time-killing.

Brutus

Form: Biped
Str:  42  Dex: 16  Con:  22  Int:  7  Wis:  10  Cha:  11
AC   40 = 10 base + 16 armor + 11 natural + 3 dex
HP: 15d10 + 90
Feats:  Power Attack, Improved Natural Attack: Claw (five times), Combat Reflexes, Stand Still

Evolutions:
Huge (10)
Limbs (2)
Limbs (2)
Claws (1)
Claws (1)
Resistance: Fire (1)
Push (1)
Improved Natural Attack: Claw (1)
Improved Natural Armor (1)
Improved Natural Armor (1)
Magic Attacks (1)
Spell Resistance (4)

Attacks:
15 BAB + 16 Str - 4 power attack = +27
+27/+27/+27/+27/+27/+27 @ 12d6 +24 damage (each)

The combination of huge size, the natural attack evolution, and five stacking natural attack feats brings his claw attack form, of which he has six, up to 12d6 damage.  They're all at max attack bonus because they're all primary attacks.  He also has 15' reach, which with Combat Reflexes means one or more attacks on most foes who try to get to attack range, which with Stand Still means they lose the ability to move.  Which in most cases translates to a total loss of a turn.  The ones that do manage to close the distance just get pushed back the next round.   Further buffed by virtually every buff spell, and he could use an amulet of mighty fists for +1 enhancement and flaming/frost/shock/corrosive, for 16d6.

I bulked his defenses a bit, though I'm not sure how well AC 40 holds up at level 20.  This can be supplemented up with Summoner buffs (Shield, Protection from ____, Barkskin, Cat's Grace, etc).  I guess this build hinges on the reading of whether the improved natural attack stuff is kosher, where improving attack "forms" applies to all claw attacks, with "claw" being a form.  I read it that way since there are other evolutions and feats and spells that explicitly affect only one attack, and figured they'd have repeated that language if they'd intended it that way.

Ranged touch attacks and will saves would eat him alive, hence the spell resistance and fire resistance, which would help mitigate incoming spells.  On top of all this you have a 20th level summoner shooting out infernal dire storks.