<<If you keep the clutch in while matching the revs, the shift won?t feel like butter, because you are forcing the synchro to spin up the transmission?s input shaft. You?ll still be able to pop that clutch out and be smooth, but it doesn?t save any wear on the synchro.>>
Sure it saves wear. You're not having to spin the engine back up to the speed the trans is spinning if you don't let it go back to idle to begin with.
Putting the tranny in neutral, revving it up, then pushing the clutch back in doesn't help anything. Just rev the engine while you're shifting, and everything will be fine.
That old way may have helped on very old, non-fully synchronized transmissions, but it has no use now.
<<You can rev match to your heart?s desire and heel and toe to all you want, but the synchros will be used to the max if the clutch is still disengaged.>>
No, they won't. If you don't match the revs, you can feel (if you know what to look for) the syncros spinning the cluster gears up to the same speed as the output shaft. If you DO match the revs, this is virtually eliminated.
In this same manner, you can shift WITHOUT the clutch. You can look at the term "double clutching" either way and not be totally wrong, but even by your definition, the first person was wrong, since their version didn't mention "blipping" the throttle while the trans was in neutral.