Delta were beaten off both EDI-ATL and EDI-JFK by a Continental who got the Scottish market in a way DL didn't. I would suggest this is simply an attempt to take as much market share as possible in year one, in an attempt to see which one of UA/AA blinks first.
Of course it may be there's room for all in high summer but outside that, Scotland has been, and remains very seasonl to North America. Any summer bloodbath on yields will affect strategic direction for the next year. i.e. "Should we redeploy this asset somewhere more profitable?"