I'm having a hard time parsing that, but no, doesn't seem like you're describing a memory leak.1
Old programs that haven't been update in multiple years with no update, plus taking up massive amount of memory along the way! Always on difference, old Intel programs that never updated, zombie software always in Rosetta!
Again, "extra memory consumption", however noticeable, on "old apps" (I'm assuming you mean "x86 apps" by that) has nothing to do with memory leaks.Extra memory consumption on old apps.
A memory leak is a technical term for a specific condition that occurs when a running process fails to free previously allocated memory due to a bug in the code or the runtime.