Sorry @LoveThe Berry - a locking system on the roller doesn't make a blind bit of difference.
The first rule of air travel is that if someone in baggage handling wants something they'll take it.
It IS nice to be reminded that most folk are good guys though and 9 times out of 10 you'll come through OK, but it's sad when that 10th time arrives ...
In the circumstances I think I'd react just like you. If I wasn't in a position to push the point and insist or move to a later plane, I'd pull the highest value items out and decide whether I could afford to gamble the rest.
It's always worth making lots of noise ! Customer service hate a big scene that draws lots of attention and shows them up. Raise your voice and refuse to hand over your kit for as long as possible. Be an obstacle, don't let them take you off to the side. It might just make them back down.
If you're travelling standby and don't have any booking or right to expect a seat and the advertised baggage allowances then you did all that you could and at least had a strong case to protect your gear in the hold.
I'll never forget waiting for my plane one time in a small airport. I was watching suitcases taken from the hold of a plane being loaded into a baggage truck out on the airfield. They put the bags onto a powered conveyor that lifted them up into the open back of the truck. When the truck was full, the driver just hopped in and drove it away. Ten suitcases that happened to be on the conveyor carried on up and happily crashed straight back down onto the tarmac -an 8 foot dead drop :-)
You've just reminded me to get some more insurance !