I suppose it's a matter of resolution. ARCONS is an IR photon counter with 44x46=2024 pixels. I don't know how that would correspond with a camera's ISO, but you can't get much better than single photons. I'd imagine it's useless to install in your ground telescope, but perhaps in a couple decades, the resolution will be scaled up to compete with current optics imaging methods.
Photon counters were not what I had in mind when you were speaking about astronomy cameras.
I remember that around 20 years ago we had 1/100th of magnitude resolution with photon counters compared to 1/10th of the CCDs (SBIG &co.)
https://arxiv.org/abs/1306.4674