This is because of the nice hefty "flat" +40 STR boost on 5 pieces giving us +200 attack power right now. This is the flat bonus I was talking about. From this point onwards, DPS will gain more and more attack power above tanks in increasing %'s.
Right now we have 1848 and the DRG has 2158. If we get another +2 per item at i360 and they get another +14 per item at i360k, and everything else increases by the same way it always has, the Dragoon will be a net 50 attack power ahead of the PLD in terms of overall gains.
The next set, if it stays the same, will increase the difference in gains to 100. Again, assuming all other gear increases in stats as they always have.
The set after that, the difference in gains will increase to 150. Then 200, then 250, then 300, so on so forth.
This scaling increase they get over tanks, and the fact that DPS can more efficiently convert Attack Power into Damage via Potency Per Second, starts out slow but adds up over time.
It's not going to a be a problem now. It won't be a problem in 4.1, or 4.2, or even 4.3 or 4.4. Maybe it won't even be a problem when 5.0 launches. But if SE's policy on how how tanks scale compared to the scaling of every other class doesn't change, we will run into the "I'm in Grit/ShO/Defiance, and spamming Aggro, and I'm losing hate!" issue.
To fix it and keep us scaling lower, they will have to continually patch in random huge stat jumps in our accessories (Like another +40 STR to all accessories at some random point for a 10 ilvl jump), or continually increase the multiplier we get to threat from increased threat abilities and our stances.
I want to get this issue raised and fixed now, because it takes SE forever to actually take action on these things. If I recall correctly, SE stated themselves they knew parry was bad as early as 3.1 or 3.2, and told us to look to 3.4 for a possible time frame. It wasn't until SB launched that anything actually happened.
We need to raise the issue now for any chance of curbing it before it becomes a massive must-be-put-out fire. It's a super slow burning problem, but a significant one.
The same thing is happening with our health pools. We will continue to get more and more hp at a faster rate than the other classes, and tuning raidwide damage to threaten us will only hurt the other classes.
It would be best for everyone if tanks were always +XX% more HP than a DPS, and -XX% lower damage than a DPS, relative to eachother. That way both raid and solo content and everything inbetween can be sensibly adjusted for a reasonable difficulty curve for all roles instead of eventually having to tailor-balance everything on a per-role basis.