I see no mention of using gear appropriate to a dive.
Uh, that's the whole point of this discussion. I see the gear I choose for a dive perfectly appropriate for my chosen dive.
I see no mention of a computer to track NDLs on a deeper dive.
Because a depth gauge/timer with tables work just fine, or a modern bottom timer w/ tables/ or a computer.
But time and depth need to be payed attention to. If someone can do that with a computer then knock yourself out.
Problem is computers have a way of making people zero in on NDL while they also look at SPG. They can lose track of actual depth and time.
I see no mention of tracking your remaining air on a deeper dive where, for example, there there may be currents or other task loading.
Pay attention, that's what they used to do and no reason it can't be done now.
I see no mention of restricting this practice to shallow dives.
That's the whole point of a discussion, and you never asked.
I dive to about 40 to 60 feet diving minimalist. If I didn't have to wear a thick wetsuit I would consider a deeper dive.
I see no mention of having any way other than an air share to help a buddy or other diver.
Practice makes perfect. I was trained to buddy breathe and
if I ever have a buddy they will have to know how to do it.
Most of the time I dive solo so it doesn't matter.
All I see is jumping/walking into the ocean with a tank, mask, and fins and a dive plan to return you to the start with 0 psi left in the tank.
And how wonderfull it is. Actually I do have air left over. By the time I get back to shore or end my dive I always have about 200 to 300 psi left. My J valve goes off at about 400 psi and I know I have a few minutes left. But when this happens it is no surprise, I 'm expecting it. I have been keeping track of time and depth and I'm ending my dive just about the time my reg starts to breath a little hard. I'm not against SPG's, I use one. I have several tanks without J's. None of my new HP tanks have J's. I could use them without an SPG if I wanted and I sometimes do.
If I use my DA Aquamaster there is no way to use an SPG.
Some people never would have made it in the old days.
I would have thrived. Unfortunately I was born 20 years too late.