All I can say is that it was an issue for me, absolutely. As I mentioned, I changed over my MB and CPU - when doing this I did a completely fresh OS install complete with all the up to date drivers. The OS and the game only are on SSD, everything else I install to my HDD's, in my area there is an excellent cable network and I score highly on Speedtest yet I still have lag spikes. As I said I had it on Ifrit and last night on KoH in WP.
I'm no network genius either, all I can testify to is having this issue, something I never experienced in other recent AAA MMORPGs such as Rift or GW2. I know my PC has enough power to run the game at max settings, but by lowering the settings it shaves time, however small, off the lag issues that I have experienced.
You say 'unless everyone is having this issue,' well I can't speak for everyone, but I can say with some confidence that in about three quarters of any DF parties I have been in, that someone has complained or apologised for lag (whether they are using that as an excuse to cover up a mistake I can't tell you), but I [genuinely] think there is something to this that merits investigation. They re-wrote the game in under three years, are you telling me there is no possibility that a corner may have been cut/not means-tested properly in an early coding stage that may have been built on now that is an underlying issue, and that is why there has not been a definitive response? Again - I stress - that is complete conjecture on my part, and I was quick to write off the lag complaints when I wasn't running dungeons all the time so I didn't see it as a problem. Now I have and I can sympathise with others, I can get on MP in BF4 and experience flawless gameplay, but I can't in FFXIV. If I'm paying a monthly sub, I would expect a level of service: do you really think a reply of 'please zoom out,' is adequate?
I enjoy this game immensely, and will no-doubt continue to play it for years to come, but I will admit I hesitate for a second before opening DF as I worry that a mistake made on my part because of this issue will cause a wipe and bring a barrage of insults and venom.