Do that with cables. Even faster with old down tube shifters. Bang a Di2 mech and you are looking at massive money to replace it. I'd love a Di2 2x12 gravel bike, but the boss said I have too many bikes, so the 2 x 10 CX bike will have to do.
It's so long since I rode down tube shifters that I can't comment. I will say though of my current bikes, ten year old cabled Cervelo, Kinesis and new Cervelo both di2, there's no way I can shift anything like as quickly with cables that I can with di2. Perhaps there's a technique I'm not aware of??
This isn't a frequent occurrence but I genuinely recall a few occasions when fast di2 shifting prevented a foot down or fall.