ESPN is currently not even a native app so it won't do much good in the dock if you want instant load as it has to go back to the phone for updates. I tried it in the dock and removed because it stunk. To make matters worse, ESPN on my iphone that has iOS10 has troubles opening a score/game in progress. Tried re-installing but it wasn't any better.
Dark Sky would work and load instantly but 15 minutes later it would start the spinning load icon...
I think these all get better once the developers update their products and fine-tune for background loading. Weather and Sports are two apps that are perfect examples of apps you want to be updating in the background - especially sports if you want current stats.
Currently, I am trying the following in the Dock:
Carrot Weather
Timer
Workout
Settings - because I like to change wrist raise on and off depending on the time or what I am doing
Calendar - until fantastical works right
The Score - testing now
Apparently, you have the 10 apps in the dock, plus the last used, plus all complications. If that is true, complications wouldn't need to be loaded in the dock but I will need to verify more.