"name a DJ who mixes like this"
Frankie Knuckles
Larry Levan
Ron Hardy
Tee Scott
every legendary disco dj and those who follow in their footsteps
listen to some of the hundreds of disco mixes on
www.deephousepage.com some are cleaner than others in the mixing department (even from the legends) but you will hear that some djs are able to do this flawlessly. Either way, it's a lot more interesting and compelling than listening to perfectly matched metronome music all night. The guys I mentioned above have a active following that goes back to the 70s, even though 3/4 of them are dead, and despite the fact that not every mix was pristine. They beat the muthafuggin box with hot music, real music, and that's what matters.
"can sound ****" "matching keys and grooves"
"mixing on the fly can be hit or miss"
Well that's the difference between doing it poorly and doing it well. Knowing your records makes all the difference. I do it all on the fly because anything else is bogus outside maybe knowing two records that blend well together. Preprogrammed sets are not djing, a monkey could do that (no offense dub haha). You have to read the vibe on every selection or you are not rocking the party. You have to know where is the appropriate place to mix a record, rather than the common house dj approach of matching the bars/beats and smoothly fading by the numbers. You also have to be able to ride the pitch control in such a way that you can keep things matched without sounding warbly. Not easy!
"bpm your records"
Bingo. This is part of knowing your records. 25+ years. Why do only old school cats know this? The kids only mix one tempo range of machine music or don't mix at all, only cut.