Yeah they definitely punch above their weight class in CPU. But the dedicated video encoder hardware is really impressive.
The last Intel Mac I had could render video reasonably well and could spit out decent quality encodings at a littler under one minute per minute of video. You could tell it was hard at work because it didn't take even a minute for the fans to be going full throttle.
The MBP I have now will do even better quality in a few minutes and you the lack of fans still makes me think it hasn't actually started the encoding yet by the time it's already done.
I remember using some of the old POWER Macs where you'd just set it to render/encode overnight because it would take that long, but even that was considered fast for 1080p video.