I don't see why you need to be EBG to do this.

A B fare puts you in E+ on UA regardless of status. Y/B/M fares qualify for E+. The UA agent is not going to do anything preferential for you because you are EBG (especially versus *G on UA) and you don't even seem to be leveraging this to get into Y+.

Also, I don't think it is unreasonable for SK to put an EBG in Y+ with an expensive B fare. I think it is another example of how SK is screwed up in their pricing scheme. Sometimes they have discounted Y fares for USD 1000 with some restrictions and sell USD 2000 B fares that don't get you into Y+. What kind of policy is that?