Moreover, you have 'intersect' on desktop. In the recent most update, lightroom introduced more specific subject masking tools, such as selecting the background, one or more of the people in the image, or even parts of the person (you can have an automask for just skin or iris or teeth, for example). Automask to stick to the boundaries is better than pencil accuracy, if that matters, and the ability to adjust the size and intensity of a brush mask through trackpad and numbers is great. You can use keyboard shortcuts to jump into any specific mask. More importantly, the masking is better in desktop. On the tone curve, you don't get a histogram behind the curve, which imo can really help you figure out where you want your points to go. Then there's actual features missing from the iPad. There's quality of life features that iPad doesn't have - mainly keyboard shortcuts to jump between tools like masking, crop, white balance, geometry etc. If you buy from the Mac App Store, you can select the 1TB option for 10~ dollars a month (region pricing may vary). If you buy off the app store, you can only select the 100GB option, which in my casual and heavy culling use case filled up within a year. The most minor is linked to where you purchase from.

So I haven't used classic, but there are a few differences between desktop and iPad.

Adobe lightroom ipad