Exactly, there is a reason all the top racers do this

It isnt only to save driveline but like i said it gives you that initial spring forward. The harder you preload the more spring you get. You really need to have a good strong clutch to do it but as long as you dont preload for an excessive amount of time before actually launching youll be fine.
I bet you with preloading the car would pull consistent low 1.6 60's even on a bad prepped track. On a good track it should get you guys in the 1.5 60's and ride out that first gear a bit more. Dont change a thing on the shifting

Yes shifting like that will break gears quicker but the time it saves on slip is worth it.