Standard concept- anything can be broken but most bike locks can be cut near-silently with boltcutters, faster than you can open them with the key. So sure, you could angle grind it, but it’s like swimming with sharks- you don’t need to beat the thief, you just need to make it harder to steal your bike than the next dude’s. You can plasma cut it or use other less common attacks, but why even bother? Somewhere nearby there’ll be a £4000 bike with no lock at all.
I’ve not angle ground one of these big chains but it took me under a minute with a 4 and a half inch cutting disc to go through a cheap Onguard u-lock a while back. With a chain you’d have to cut both sides of the link, and the chainlinks are 16mm of steel rather than 14mm including rubberised coating on that lock, so each side’ll be slower.
