I didn't notice the point at which this turned into a discussion about RAII or whatever a GC is in 1990's books' definitions. And why would an arena not be manual memory management if I make explicit allocations that make explicit use of such arena, and I free the arena on a suitable occasion? I'm even likely to write the arena myself, but not necessarily.
I have this simple and (in my mind) very useful equation of manual memory management ~ writing code to manage memory. Conversely, GC ~ using an external runtime (such as that in JRE) that helps you to avoid writing any memory management code at the cost of giving up control. Ok, let's lose a sentence about ARC, I don't care if you name it GC or not, and I don't use it.
I'm not interested in other pointless taxonomic discussions. Whatever, man.
Because many languages with GC do offer the necessary tooling for doing low level memory management if one so desires, while still enjoying some safety.
Naturally the anti-GC crowd rather switches to their error prone C code instead.
Thankfully that is not where the industry is going, eventually looms will be the dominating force, one generation at a time.
At this point you're almost doing manual memory management.