Can someone give me an in-depth explanation why Summoner is arguably the worst DPS?

[Sunako]

My point was that a list of ways BLMs support the group should not include Virus and Eye for an Eye.

And the reason? Because those are cross class skills? I did not say those skills are huge support. Even small support is support and better than nothing. Your statement is almost same than that Raging Strikes should not include damage increasing ability for SMN or BLM. Or invigorate should not include tp generating ability for bards/ninjas/monks.