Oddly, when I started using fountain pens, I naturally switched back to cursive since it is easier to write that way with a fountain pen, and now my writing is pretty good.
This is interesting! I think the tools we use definitely affect what we do, and these days, most people don't know how to use a pen properly. I notice it in kids who spend a lot of time on phones, that they aren't able to "shade" using a pencil - they are far too heavy-handed.
Generally I try to be supportive of teachers, but a teacher digging in her heels like that in support of a dumb policy needs to be stood up to.
Some teachers deserve support, some don't.