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

[Viridiana]

For real or troll? xD

Being a huge burden to heal is a glaring difference.

SMN have not been below in DPS for patch after patch. And DRG in no world got fixed quickly.

27 October to 9 December. That was how long DRG was a burden in FCoB. That's a day over 5 weeks. Unless you're going to try to count all of SCoB or something. Meanwhile, SMN has been a burden for the last, oh, I dunno, 17 weeks. That's over three times as long. And Kona, you're still ignoring the fact that i130 gear was always going to solve DRG's being a burden.

Editing to add in times for WAR and BLM:

WAR was in a bad spot from launch to 2.1. 20 August to 14 December is 16 weeks. That's faster than SMN if SMN were fixed with tonight's maintenance. BLM was lacking in SCOB from 26 March to 7 July. That's less than 14 weeks; which, again, is faster than SMN would be if SMN were fixed tonight. And by comparison, DRG took 5 weeks. So, yes, compared to the other two, DRG was fixed quickly. And if SMN has to wait for 3.0 it'll be a bit over 20 weeks to fix one class.