First your not you are 4 successful pvp players who are coming from that perspective, which is fine I agree with a lot of what you said, but until you present the promised PvE slant or at least someone whose focus is support/healing I don't consider you as the representation of the ESO community.
One thing I really liked is how King Richard said that you have created this meta which doesn't match what I think was the developers intent. When you make healing not really requiring targeting, and the ones that do are all positional, make skills that benefit large groups defensively and have skills that stack damage the more you use that particular skill this is the game you will get. I do think there are somethings you can do to make that are simple and begin to allow the meta of the 1vX possible.
The first idea I had was to make each keep a semi instance grouped battle ground. So how you would do this is to allow a certain number of players on both sides based on criteria. For the siege group bring back forward camps which allow 10 people to use them to be in that instance, they would have to be at least 500 meters from the keep and there would only be 3 forward camps allowed. In addition they would have a finite time period of 20 minutes so if you couldn't complete the siege in twenty minutes the timer would reset with the loss of the camp. For the owner of the keep have the same 30 person limitation but tie that into the farm if you don't have it then you can only have 10 people defending that keep. Also make siege/repair equipment tied into the mine and lumber mill, so if you don't hold the mine only 10 repair kits would be available if you do 100 would be available. The lumber mill would effect the number of siege engines you could produce 10 without it 30 with it. By making these points of interest it would force people to spread out in smaller groups to take/protect them.
I liked the comments on using actual timed jail as a deterrent for ganking in the justice system when we actually get to see that aspect. Another thing to get around the mentioned killing of crafters causing them to lost materials and items is to finally implement guild hall/housing. It of course will not be based on Skyrim of a single house available in a town but with the use of portal the idea of instance housing would not be lore breaking. I also think that the implementation of the pvp justice system must be a core update not a DLC I feel it would be very unfair to the community to release the second half of promised content that will fundamentally move the game forward behind a pay wall. I just really think it would be a huge thing that is a pivot point on whether people will continue in this universe or move on to things coming down the road.
My final thought is that ZOS needs to stop thinking of updates as pvp or pve based. Both system are in your game and there is the basis for both to be strong systems. I am greatly disappointed that no arena type system is to be included in Orsinium, to me it would fit so well with the lore of the Orcs as beating the hell out of each other seems a very orcish thing. The comments Sypher made about the itemization where spot on by limiting the path to get competitive gear to the one type of game play it is forcing people to play in a way they might not like with the end result that they won't play that content or maybe even the game you are working hard to make.