[michaelt]

> It took the guy longer than I expected with an angle grinder, made a lot of noise, sparks flying, etc.

Your guy was probably being very careful not to damage your bike. With the right tool, even top-quality locks with hardened boron-carbide shackles can be cut in seconds: https://youtu.be/cbYVmRNzGLc?t=368

> Someone highly motivated could lift the bike into a van, drive home, and then worry about cutting off the lock. It just seems a bit far-fetched.

One mode of bike theft in the UK is: A white van pulls up to the university/train station cycle racks, men with bolt cutters grab as many as they can in 3 minutes or so, then drive off.

As they're going for volume rather than quality, the bikes with the worst locks are the first to go.