DF and DP will have been out for one full year. Never before have we had to wait a full year between brand new operations.
True, although other than at the very launch when both EV and KP were introduced (at least I think they were released at the same time), we've never had two operations released at once like we did with DF and DP. Not even with Makeb did we get two new operations unless you count TC which is one boss, no trash (unless you count adds that spawn during the boss fight and the isos that people damage and relocate before fighting the boss), and takes 10 minutes. S&V was the only new operation. TFB was reconfigured from level 50 to level 55, which I don't consider as a new op, just recycling old content and supposedly increasing the difficulty.
Personally, I don't see much difference in difficulty between former 50 SM TFB and 55 SM TFB except for more HP. They certainly don't hit harder, or if they do, it's impossible to tell it in level 55 gear. EC HM is more challenging than TFB SM for people in 72's or higher. And NOT
counting the 4 highest-end raids (NiM S&V and TFB, HM DF and DP), I'd say that the most difficult ops fights are (#1) 8 M HM Operator IX from TFB and (#2) 16 M SM Dread Council. I don't know why, but 16 M HM Operator IX is so much easier than 8 M and 8 M SM Dread Council is so much easier than 16 M. I do not know for certain, but I have a theory for this. It is my opinion that 8 M and 16 M Operator IX are the exact same boss fight in every way except that only half as many people can go in for 8 M obviously so each and every player in 8 M essentially has to do the work that 2 people in 16 M would do; and while the difficulty of the bosses themselves is proportional for both the 8 M and 16 M versions of Dread Council, there are just so many mechanics for a SM fight that it is so easy to become confused / distracted with the 8 additional players in 16 M and stray from the correct strategy, whereas in 8 M it is easier to focus on mechanics since there are fewer other players.