Pfft. I had a medium-grade bike lock in college, and I once accidentally stole a bike because somebody with the same color/model/lock parked in front of the same building as me. My key was a bit stiff and I kind of had to force it, but it worked fine. I just remember thinking "why does this seat feel different?" Took me a couple of days to figure it out. I put it back- sure hope the original owner came and looked again after his initial disappointment that day.

There are bike locks that do mostly defeat angle grinders. They are not cheap, of course.

https://www.youtube.com/watch?v=SpVOTEOMRuE

https://www.amazon.com/Kryptonite-Evolution-Integrated-Chain...

I don't know why you would link a video instead of saying the sentence "chain locks are hard to cut with an angle grinder because the chains are hard to hold steady"

I forgot to add that clarification, thanks.

Ref: https://m.youtube.com/watch?v=aBxyaFf379g&t=1m4s

Tl;dr if your lock doesn't double-lock (both sides) and have a cut-resistant core, it's only stopping people who can't afford a Ryobi angle grinder