That is an extreme simplification. Modern crud apps run from essentially any network in the world on hardware of every conceivable form factor and vendor. The protocol is open and so obvious it is routinely taught to middle school children.
All of those things are significantly different than a mainframe/term setup
I disagree. TN3270 runs on essentially any network in the world, and has existed for quite some time. I am scoping this down to CRUD apps that are text and labels.
I'm currently on my phone on a streetcar in San Francisco. I'm pretty confident there's one of those platforms I could access now with the greatest of ease, and the other would take some doing.
All of those things are significantly different than a mainframe/term setup