Who cares about t 0.5 times? A child who doesn’t know what they are but knows shorter is better?
How about one who holds a doctorate in electrical engineering, with focus on telecommunication, who designed and built communication devices which went into commercial production, and therefore knows, that this t0.5 time is very relevant for estimating the relevant time frame for light output.
If, for whatever reason, you want 1/2000s exposure time, then a flash is a perfect fit, if it outputs most of its light power (even 75% is good) within this short time frame. BTW Profoto does list t0.1 time, it is irrelevant here, though.
I am instantly suspicious of any flash company that quotes t0.5 times, the tail is always longer than the initial burst so a t0.1 of slower than 1/500 is nothing to boast about. My Einsteins at 1/4 the cost and more power are 1/360 sec at full power and have incredibly short durations off full power. Seriously, who is doing this set in TTL? I use ETTL when it is appropriate and think it is very good, but do you know the algorithm they use to reduce fill rating as EV changes? Nobody outside Canon does, you can’t do this stuff in TTL!
I don't have such a flash unit myself, but I know folks who have this one, or a Chinese knockoff, and they use it extensively in this airTTL mode. Apparently it works, like it or not.
Your Einsteins may be the best product line ever, and you may be the smartest person in the world for using them (at least as long as you don't write nonsense about the relevance of t0.5 times), but there are indeed people who want to shoot wide open and outdoors.
My point, that nobody seems to be taking up, is this, if your ambient exposure is 1/2000 sec then you are trying to mitigate a lot of light, to do that you need a lot of flash power to be brighter than that. I don’t know of an affordable system that can do that so I am asking, what, specifically, are people going to use to shoot with a 1/2000 sync speed?
I did the calculations a while back: direct sunlight is comparable to 5000W incandescent light from a directed source (think construction light) held at 1m distance. Put it at 3m distance and you'd need 50.000W. If you have a shutter time of only 1/2000s, we're talking 25J sunlight here. If you start with two of these 500J flashes, turn them down to half power to make light output fill the 1/2000s shutter time, then you still have 300 - 500J at your subject. If that's not enough, I don't know what is.