I agree with you in the sense that caster DPS is dependend on other jobs most of the time in order to do very well. However, the raw damage on a BLM (which was tested by Judge Zero) is 10% higher! It was even more than that. In end gaming this translates in BLM having 50DPS more. Tailoring gear isn't going to close that gap, especially not since BLM has better utility. Everything a Summoner has, is something not worth using by the class unless is very exeptional cases.
I would just delete the raise and let Summoner do more damage than a Black mage (at least in ST). You have not refuted the fact that Black mage has:

Better AoE
Better Single target
Better utility
Better burst
Better scaling of gear.

The only thing you have adressed is the gear issue. It is a legitimate concern, but it will in no way or shape revive Summoner. At best, if you tailor gear to Summoner, BLM will still have:

Better AoE
Arguably better ST
Better utility
Better burst

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