OK, now that Summoners are able to keep spirits out and recover MP with merits, there must be more done to improve their performance:
1) Updated spell lists. Any BLM who gnashes his teeth over this needs to be ignored. Tier V spells, Comet, and the appropriate enfeebles (Addle, Break, etc.) need to be a part of the spirits' spellbooks.
2) Avatar-quality MAB.
3) Split casting times between enfeebles and elemental spells.