Somebody please explain! Why X-E1 JPEGS are darker?

No where in my post did I ever state whether my exposures were made in an auto or manual mode when comparing a 500D to a 7D to my X100.  I've shot plenty of manual in the 30+ years I've been shooting and understand how to underexpose (or overexpose) by 1/3 stop even shooting in manual mode by either adjusting aperture, shutter speed or ISO.

That being said, there is nothing wrong with the sensor or the metering in the Fuji.  Fuji's metering and exposures are close to spot on usually.  The issue with the OP's images is a fault of the system in the 550D.  This camera line notoriously overexposes by 1/3 to 1/2 stop in any mode. Even with the same settings under the same lighting the Canon images will look overexposed because they are overexposed.  If shooting in an auto mode it is corrected by dialing -1/3 EV and if shooting in manual I would compensate by opening up 1/3 stop on the aperture or adjusting the shutter speed or ISO as required.

To the OP, try shooting the same scene. Then make an additional exposure on the 550D underexposing by 1/3 to 1/2 stop.  You will find they more than likely will match your XE-1 exposures.

Scott