Yeah, people look at maximum, rather than what is average, and what is above average. (When giving "advice" on what DPS they should be doing.)
Most of the time, the best food, raid buffs, and the best potions make a difference. Along with some lucky line ups in RNG.
An example, my average DPS could be 4.3k at i340 in O6S. Use my cheap food (+35 stats) and cheap Mega Potions, my DPS usually goes up 300 points. Im sure with the best food/potions, I could have been 5k at i340 my 1st clear on O6s. (my last clear, with +45 stat food, and 2 HQ mega potions, was 4.9k DPS) So get some good stuff, if you really wanna raise your DPS, and not be cheap like me. (For comparison, a BLM with similar gear/food as me, did 7k DPS in that clear, DRG tied me, and the BRD did 4.6k with slightly better food than me.)
3k is passable for O1S, but not really passable for O2S+
I think you need 3.5k for O2S, and then closer to 4k+ for O3S and on.
Depending on other factors, u might find urself unable to turret during mechanics which is where most of your DPS loss will be.
Swift cast for those moments, and find the absolute maximum amount of time u can sit still, to try and get that last spell off, so you can dual cast while dodging. (in my case, 90% of all mechanics happen AFTER a dual cast, and require a hard cast, and will hit me if i let the cast bar get to 70%, and only 10% of the time will the cast finish, even if i let it get to 70%, and start running. This alone makes my DPS drop, and i use cheaper food/potions)
with no movement, I can do 5k DPS, but in movement heavy fights, my DPS can drop to 4.4k - 4.8k depending. (Usually includes rezzes/cures so idk, and i usually dont use food/pots in practice.)
but this was in i340-i345 gear.
in i340 gear on O4S, i struggled to get 4k DPS, due to all mechanics lining up at absolute horrible times. (always near the end of a GCD for hard casting.)
my group changed our strategy, so i didnt have to move as much, and if i was lucky enough on the hard casts in 1 part of the fight, my DPS would be 4-4.4k
ONCE my procs actually landed decently and i could use my CDs before the boss would jump away, which lead to nearly 4.8k, but we wiped. (actually almost ever clear, was usually an unlucky run for me, but all my good runs, we never clear :P )