would that be useful, or was it ever proposed? I successfuly parked ambulance got into it, and grenaded myself to cesar, so cutscene played, and I stand sniping on enemies. With more practice I think it would be possible with smaller car, or even without (not 100% sure).

Funny strat. :D I managed to make it without a vehicle way back when I thought of it myself but it is very hard. Getting a vehicle for the jump would be slow... For a conveniently placed vehicle from traffic, it takes 8s from gaining control after the cutscene to standing on the car roof. That is as slow as running up. And you haven't done the jump, yet. So we are talking about car-less or nothing.

It took me 4s to do a satchel jump up (not successful, but the successful ones do not take longer or shorter). That is just 4s faster than running up. The loss of armor is a downside. You'd have to jump off your bike and let it roll outside the despawn area (the one that the current route evades by parking on the top of the building you snipe them from) and then run back to the Pier 69 marker.

I am not sure if the "rolling bike out of the despawn area" strat is faster than the "drive up the stairs" strat so I cannot tell if forcing that is a further time gain or a time loss.

I do not feel like doing proper testing for this, I am "busy" with duping stuff and will be for quite some time. I hope you ares still by my answer. ^^ Whatever the results will be, I think only satchel jump enthusiasts will put in the vast amount of practice / reference point search required for it.

This would be hard to do because most of the time you would just kill yourself in the process, and even if you didn't die, your health would still be very low that you would probably die when driving to t-bone or sniping ryder.

Oh man, this is complicated. I do not know if saving for health after Snail Trail is worth it. For bad/decent runners, probably, but this strat is only for the pros anyways.

If you do save after Snail Trail, then the 80% hp loss is not too bad in the short term because you have 80% or so health left and 20% armor, that is enough for P69, Toreno's Last Flight, and Yay-Ka Boom Boom, but you will miss your armor in LV.