Tried Denmark recently, totally agree that in humand hands they seem to be unfair... We were playing immortal, but that was pangea and 20 civs and my friend was 3 policies ahead copmared to the leading AI in middle ages and he had everything built in every city. However, based on my experience, Denmark usually performs bad in AI hands too.
I'd vote for removing +2

and/or 25

boost from jelling stones. Not a big deal for AI, but a big nerf for human
EDIT: I changed my opinion, proposal above is bad, cause AI fights way worse than human. Actually it should be the opposite. I currently think of +3

/+3

for killing units and additional +2

from jelling stones