I'm having trouble picturing this. Not trying to give you a hard time. But if your elbows are locked at 90 degrees then how do you move your hands? I would love a little more explanation. I like to learn about other people's techniques.
I tend to keep everything below my elbows locked, i.e. hands and wrists. My movement comes from my shoulders pushing and pulling my locked wrists back and forth. My elbows end up bending back and forth quite a bit. My core stays still. Standing at an appropriate height kitchen counter this feels quite natural. Sitting is a little more awkward but necessary as I have increasingly strict physical limitations on my standing time. I have a workbench set up with an adjustable vise over a water/oil bath and a bench stool that gives me a lot of flexibility if I am doing a lot of work. But I don't have any issue adapting to what is available.
And kind of unrelated, but sharpening in-hand is where I feel like I have the most precise angle control. I can do that sitting or standing or laying down or upside down. But I definitely couldn't do it with my elbows locked at 90 .