That's not necessarily an invalid comparison. From a technical perspective, NVIDIA's NVENC encoders for example have been able to compress H.264 with similar efficiency to x264's slow preset at several times the speed for a few years now.
And there's also the fact that for many purposes, it simply doesn't matter. Filmmakers often don't want an impeccably compressed, low-bitrate output ready for streaming directly, they want an output with the highest quality they can get, as fast as they can get it and don't really care how high the bitrate is as long as it's reasonable.
In use-cases like that, a faster render/encode is what's valuable and it doesn't really matter which processor is used to produce it.
Well, what are the encoding settings of one vs the other? If the iPhone is encoding, to say, 2.000kbps and the iMac is encoding to 20.000kbps, the iMac will definitely take longer to encode.
It seems, to me, that the iPhone is just creating a new copy of the file. I'm not saying that's what's happening, but what it looks like compared to the iMac.
He is using Sony software on the iMac and Apple's own iMovie on iPhone. iMovie for macOS and iOS has always been ridiculously fast, even on a 2011 MacBook Air.
Perhaps, a better comparison would be to compare iMovie on iMac VS iMovie on iPhone 12.
That’s one step closer, but it all depends on what exactly you want to test and compare. If you want to test raw speed you probably need to use comparable transcoders.
It's amazing how nobody flags these garbage twitter posts endlessly fawning over the Apple prison complex with fake benchmarks and yet one guy posts "Farewell, macOS" yesterday [0] and it got flagged immediately.