Also wind patterns. At the midlatitudes westerlies dominate. So the east coast has a continental climate (receives cold air in the winters, hot air in the summers) while the west coast does not (the oceans make the summers and winters mild)

You’ll see that the west coast cities on the same latitudes of their European counterparts have a very similar climate (as opposed to east coast cities, which have a very different climate than their latitude-counterpart).

Amazing. Where did you read this?

A large part of it is also simply the fact that at the midlatitudes westerlies dominate, which means that western Europe receives mild air from the ocean, while the US east cost receives more extreme weather from the continent.