Eidolon: T4 by itself. 2/3 spellcasting: Low T3 by itself. Summon Spells: Eh... I want to say T3 by itself, until I see an argument for something gamebreaking. There are ways to abuse CW Samurai, too, but that doesn't put it into a tier of potential gamebreakers. Just like the Druid would still be T1 if it just had the spellcasting, Summoners don't break out of T3 just because they have more T3/4 features. They are very nice out of the box, though... something which the tier system has trouble describing.