I don't think that the OS (itself) RAM usage is necessarily much different (although nobody has exact data, so anybody here is speculating). However on MacOS apps can use much more RAM if they want, while iPadOS ejects stuff from RAM when necessary and the apps that use a lot of RAM are not many and the developer has to ask specifically to be allowed to use more RAM. Browsers for instance on iPadOS have a relatively low cap, that's why they reload exactly the same on 8GB and 16GB devices (I have both and have compared them several times).
How Apple Intellingence will impact reloads on 8GB devices is still too early to know.