@lickthetoad – I understand why you think that, but in fact they are the ones doing it wrong ;).
There is only one way to add fields to those forms in a compatible manor. This is a limitation of WP core itself, but some crafy devs came up with a solution sometime ago. They all used the same override to core that included a new hook to render fields.
We use that and are compatible with hundreds of themes and other plugins that also use it as well.
You can read more about it here https://docs.wppopupmaker.com/article/297-popup-maker-is-overwriting-my-menu-editor-functions-how-can-i-fix-this
Tyvm for the fast answer.
I will post a bug report to the theme support theme.
Regards