Synchros in a synchromesh transmission have to either speed up or slow down the next gear you are going into (depending on whether you are down or up shifting) before actual engagement is allowed.
If you try to force the engagement before this happens you can wear out the synchro rings or break their teeth or bend a shift rail or fork.
It's like now with your long shifter, when you shift from 3 to 4 you have to go click click, try to go slam one time and you'll see you can't do it. You can go click click pretty fast but it does take a second.
Short throws are worthwhile, and you can shift faster, but you will still be limited by the spin up time of the next gear that at the moment is just freewheeling. You are fixing to lock that freewheeling gear to the output shaft and the cone clutch brings it up to shaft speed THEN lets it engage. Race cars probably are not synchromesh. They are probably just constant mesh.
Now if you shift at just the right moment, you can cause little or no spin up to be necessary and shift faster flying straight through neutral; synchromesh transmissions allow for a lot of errors in that "right moment".
If you've got one of those long notchy shifters, I've heard that putting a heavy knob on them will really help. My 98 S-10 is not notchy at all. This girl I know calls mine a slapshift (whatever that is) and tells me don't be shifting her car like I shift my truck...
In a synchromesh gearbox, to correctly match the speed of the gear to that of the shaft as the gear is engaged the collar initially applies a force to a cone-shaped brass clutch attached to the gear, which brings the speeds to match prior to the collar locking into place. The collar is prevented from bridging the locking rings when the speeds are mismatched by synchro rings (also called blocker rings or baulk rings, the latter being spelled balk
in the U.S.). The synchro ring rotates slightly due to the frictional torque from the cone clutch. In this position, the dog clutch is prevented from engaging. The brass clutch ring gradually causes parts to spin at the same speed. When they do spin the same speed, there is no more torque from the cone clutch and the dog clutch is allowed to fall in to engagement. In a modern gearbox, the action of all of these components is so smooth and fast it is hardly noticed.