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

[Sen_Terrechant]

I am actually a little outraged, I just did some parsing again (5 attempts on both SMN) ilvl 125 with 115 weapon. BLM = 502 on average / SMN = 457 on average over a 6-7 minute parse. And on my SMN I even used poison pots in my contagion, like seriously?

Sounds about right.

We have great DPS up until that 4ish minute mark and then bam, drops like a friggin rock.