Bioware/EA is managing expectations badly. It is not unreasonable for last gen console owners to expect that the dlc for the base game would continue on their systems.
That being said, PC and current gen (XBox1 and PS4) owners feel that in supporting that old hardware that their experience is being lessen (in terms of content and graphics) and that their hardware is not being used to a fuller capacity.
When Bioware/EA made the decision to support the old console hardware it may have been a correct decision at the time. Probably somewhere in development Bioware came to the realization that it was not going to work as well as Bioware thought. Plans had to be changed. Content may have been removed or downgraded to fit the old hardware.
Since Bioware wanted the same content across all platforms certain content may have been removed from the base game that the PC and Current gen consoles would have no problem with.
The last gen consoles have had nothing but problems with the game. Not saying that PC and current gen did not have issues, but from what I can tell nowhere near the problems of last gen owners.
I questioned Bioware/EA's decision to support last gen consoles since there was no way a ten year old computer would be able to run the game adequately or period for that matter.
So Bioware/EA has made another business decision that has angered the last gen console owners. No more dlc for last gen consoles. Is it fair probably not, but a lot of business decisions are not fair.
As far as Bioware/EA screwing the last gen console owners that is not correct. Bioware is only responsible for what it has delivered. Did Bioware deliver the game on the last gen consoles as promised? Yes Bioware did. Bioware still is responsible for making sure that the base game works properly. Did Bioware deliver the dlc Jaws of Hakkon and other dlc to date for last gen consoles? Yes Bioware did.
Is Bioware/EA morally and/or legally responsible to provide future dlc for last gen consoles. The answer is no. Bioware/EA is not bound to provide dlc for any platform. Is Bioware/EA legally and /or morally responsible to provide a XB1 or PS4 version of DAI to last gen owners? The answer is no. The last gen owners received what they paid for. Bioware/EA is legally bound to fix any problems with what was purchased.
Would it be a nice goodwill gesture if Bioware/EA did? Sure it would be.
Before anyone states that you are probably a PC, XB1 or PS4 owner I was not. My computer did not have the horsepower to run the game. Neither did my work computer. I spent the first four months after release playing on my daughter's laptop while she was at work or school.
My job finally upgraded my work laptop so I can play the game reasonably on that machine.
Eventually I will purchase a new system, but playing video games is not my primary concern. I play games as a hobby. I buy computers for my vocation.
Everything here is my own opinion, YMMV