It's possible to talk about "The Average Redditor" or "The Average New Yorker" or "The Average Tokyo Resident", because statistics isn't about community, but the whole reason Reddit has survived at the size it is is precisely because subreddits allow different people to have vastly different views of "what's on Reddit" based on subscription/unsubscription. This allows The_Donald and EnoughTrumpSpam and dozens of other communities which would fight like cats in a sack were they ever mixed to share the same service.
So Reddit isn't a community. It's a pre-made hosted platform to build a community meeting point that you can largely (or completely, via invitation-only private subreddits) insulate from all the other communities on the same platform.
So I think it's valid to refer to "The Reddit Community", with some caution, because there is a familiarity with some of the same content, and an ability to relate in certain modes of thinking. The same way as "The Tokyo Community" generally familiar with Shibuya crossing, the local weather patterns, and behavioral expectations.
There's significant standard deviation, but also a commonality that enables a stronger connection to other members of the platform / city.
It actually makes me appreciate Reddit a bit more -- it can be garbage, but it's also a bit of a centralized meeting place for so many smaller communities. Even if the bulk of those smaller communities doesn't take place on Reddit itself, they still flow through Reddit.
Reddit is like the central bazaar of discoverability. The community you end up in might not live on Reddit, but in all likelihood, you discovered it through Reddit.
So despite how terrible the big communities can be (which is not a Reddit-exclusive problem), I'm still glad it exists. Maybe an alternative is needed, but at the very least, I respect how Reddit has mostly retained this unique ability over the years.