I think it's a very good point that a failure may not be obvious on power on but cause irrecoverable problems during a flight. With electronics there are no guarantees, you could power something off incorrectly 100 times in a row and it would work fine or you could do it once and kill it. I've worked with technology for many years and seen numerous devices survive unexpected power cut outs but I've seen a small number that haven't, it feels like Russian roulette.
Aside from the risk I'm not understanding how what the OP is proposing is significantly quicker. The
Mavic 2 is quick to power down so yanking the battery straight off is going to save at most two seconds as opposed to double pressing power to shut the drone down properly. I'm not understanding how 'powering on' the battery saves any time at all, you're going to need to press the power button anyway and the drone is still going to need time to power up. On a battery change a couple of seconds is nothing against the amount of time the drone needs to land and then take off and fly back to its position which is going to be unchanged.
If the required function is so critical to risk an expensive drone to save a couple of seconds it makes no sense to be using one drone with a risky process, I'd have two and swap them over at different times if it was that important. And if the footage was important I wouldn't be trying to cut corners I'd be double checking everything is right before take off, there are numerous crashes and problems on the crash/flyaway forum where people took off prematurely or didn't do some basic checks which in the air became a problem that they couldn't recover from.