Feel free to yell at me for this guys because I'm trying to hammer things out for myself, but I thought ascent rates by and large weren't an issue for CESAs? The idea being that it's better to be bent than dead?
A bit of smart simple/ quick calculation behind a CESA is important too for ascent rates, the chances of this happening at the beginning (equipment failure) or the end/ far off close to your NDL (OOA) are probably higher. If you've just started your diving, the only factor on "racing to the surface" provided you've only been in the water a couple of minutes would be lung over expansion to which, exhale as you're using your solid state rocket boosters to blow to the surface. If it's from an OOA at the CESA depth towards the end of your dive, the chances are you've not off-gassed enough to safely hit 60fpm ascent rate at a depth of 20ft. I'd assume this would be something that happens for running out of air on a safety stop; is it ever worth it to run out of air when you're not directly threatened by deco obligations- probably not.
Frankly speaking teaching CESA's to me sound like a comfort thing for newer divers. Our natural reaction if we run out of air completely and no one is there to assist is to surface (or to try and bend around enough to kiss your arse goodbye), CESA's train you to surface at speed. It would make more sense to train divers to respond more to receiving air shares and swimming to your buddy. Horizontal leads to less dangers related to speed than vertical anyways. More emphasis should be put on the need not to perform CESA's and similar events in team diving because your team should be useful in non-emergencies, let alone during. I think it's curious for organizations who train you to stay in the water, no matter what to deem a phrase "Controlled Emergency Ascents" from 1/3 of what you're probably diving anyways.
