When you shift at the same time you put in the clutch the shaft isnt going to slow down nearly as much as it does on a normal shift. It may seem fast, but the 2-3 especially takes some time. Looking in the datalogs, it typically takes me 50% more time to shift 2-3 than 1-2 or 3-4. For normal transmissions this doesnt matter either way, since the synchros work.
Also consider that if you do this properly there is no need to use the clutch the second time.
I still use it to prevent further wear. But with the 2g I probably spent a combined 3 months at least driving with no clutch at all over various busted hydraulic events. The process is the same just no clutch. With no clutch being used the input shaft will always be at engine speed, so the only thing lieft is the timing, either in the pause in nuetral when upshifting, or the rev match on the downshift. IF you get it wrong with no clutch you stand to lose a lot more. The synchros have to deal with the whole weight of the engines rotating assembly rather than just the input shaft
But I'm probably OT now...