And yet they nailed down the latency to be surprisingly low, it was much better than Parsec I used at the time on LAN, with NVIDIA datacenter being at 25 ms instead of the 5 ms it is at today (and people in the city it's at have it at sweet 1 ms) 

Of course there's a lot to dislike about the service and the trend overall, such as the recently inflated outrageous pricing, but from technical standpoint I was surprised how well it worked, with me being rather sensitive to latency. You're probably right there's more latency between mouse and the monitor already, but that also means the network doesn't necessarily add that much on top... 

I think what Missphant was asking wasn't "what is input latency" but was "does flatpak introduce more input latency than a 'normal' application". Unfortunately, after a quick search I didn't find any benchmarks. (I didn't look very thoroughly.)