1. Not good
2. I have fiber
Obviously generalization and I don’t care if someone has 2008 DSL and it “runs awesome”.
I assume they don't release in markets that aren't physically close to the hardware though - it's not available at all here in New Zealand for example.
mobile broadband can easily have 20-30 ms latency to the ISP.
DSL is often 10-20 ms. Coax is in the same range, depending ont he provider.
Fiber is usually 1-3 ms.
On Chrome on PC with a low-latency gaming monitor, you can notice the difference if you play a game natively and then stream it, but honestly you stop thinking about it pretty quickly as long as your ping is under ~25 ms or so. I'm loving Cyberpunk on Stadia and I've been playing shooters on PC since MoH:AA in 2002.
Edit: I have Comcast Cable, not fiber.