As a long time Mac user, MDI has always felt like a stopgap to make up for the OS not having the ability to manage windows on a per-application basis (so for example, being able to hide all windows belonging to a particular application or move them all to another desktop/screen).
It also feels very foreign on macOS - Photoshop suddenly gained the MDI-type UI in like CS4 or something, after having let windows and palettes roam free on macs since Photoshop’s inception. I always turn it off, feels claustrophobic somehow.