The Denon is a receiver, although I believe you can turn off the amps and use it in pre-processor mode. I'd say the core differences between Denon/Marantz gear and Arcam gear is that the former is cheaper and will probably still work perfectly in 5 years.
The nearest competitor in my opinion, as I said, is the Rotel 1576 MKII, which has a similar feature set to the AV40, most notably full Dirac room correction. I investigated rather superficially, but I believe it lacks eARC, streaming, and I'm not sure if it has Dolby Vision pass-through. Unlike the Arcam it does have a balanced analog input, and multichannel input.
The Rotel's published SINAD (112) is better than Arcam's published and much better than Arcam's measured. But we have no measurements on the Rotel so the figure should probably be treated as wishful thinking.
Here where I live the Rotel is a cool 1k Swiss francs cheaper than the AV40, which one could put into a streamer and an eARC gizmo. That's what I'd do, if I wanted to spend 4k on an AV processor.
Then there's Anthem's AVM70 and its basically endless list of bugs and issues for those brave pioneers interested in the train wreck type of audio experience. I'd rather watch it from afar, on the news if possible. And be aware that its previous incarnation, the AVM60, was declared basically broken when measured, it's that badly engineered. None of this surprises me, after dealing with Anthem.
So these are the options. Personally I would not touch this AV40 despite the excellent impression it left on our host.