Level 1: Half Spellcasting, Inspirations (Pseudo Ability), Inspire Courage, Archetype (Minor)
2-2.5 abilities. Inspiration itself is a non-ability, Half Spellcasting at this level is essentially two cantrips so its value is fairly low at the moment, but I'm happy with a slightly stronger start to a class.
Level 2: Inspire Competence, Sonic Resistance 5, Half Spellcasting
Sonic Resistance 5 is half as potent as the Warlock equivalent, so this is about two abilities.
Level 3: Words of Power, Half Spellcasting, Moderate Archetype
Depending on the potency of the Archetype ability when they've been rendered approximately even, this is about two again, you're right that WoP isn't especially powerful.
Level 4: Inspire Health, Half Spellcasting.
One and a half abilities, casting just hit 2nd level spells though, which is a decent boost for the Poet.
Level 5: Charmed Life, Sonic Resist +5, Half Spellcasting
Two abilities again.
Level 6: Archetype power (Major), Half Spellcasting.
Half, plus capstone.
As an alternative, Sonic Resist +5 could be level 2, 4 and 6, and something else small but neat could go into level 5.