Good account of your success and the approach you took is basically the way it works. I am not sure I would have dared use a garden hose on a client property but it makes some sense.
The reason your drywall underneath looked brand new is it was probably never primed. Most popcorn ceilings were a mix of cheap ceiling paint and the texture sprayed over non-taped and non-mudded ceiling drywall.
It sounds like somebody got a coat of decent paint on one of your ceilings so it would have been harder to saturate.
And your advice to use a nice wide blade is dead on.
I wish I could say the task of removing them gets to be more fun as you do more and more of them but
They really are the work of the devil.
Oh well, you will be so glad you got rid of them. Nice job!