Even with "Reduce Transparency" enabled (blur disabled) I've had times when Mission Control operates at 2 frames per second on my 13" 2013 rMBP. This never happened using Mavericks.
If you try full screen zoom on Yosemite with an external display attached, it's similarly unusable.
If you try full screen zoom on Yosemite with an external display attached, it's similarly unusable.