Are H.264 proxy files really that bad anymore?

I've always proxied my rushes as ProRes 422 Proxy; however, I'm in a situation where I require proxy files to have a lower bitrate than what ProRes 422 Proxy can deliver.

I tried proxying my rushes as H.264s at 20Mbps at the default keyframe interval of 72. And the experience was as expected: scrubbing and playback was stuttery and laggy. However, when I proxied them again at the lowest keyframe interval of 1, the playback and scrubbing was as good as ProRes 422 Proxy. The bitrate and file size ~10 times smaller than the ProRes 422 Proxy files.

So it begs to ask the question, with new computers such as the M1 MacBook Pro, is editing with H.264 proxies (at a low keyframe interval) really that bad?

The only downsides I can see with this workflow are:
- Transcoding takes ~5% longer, and
- At 20Mbps, the image quality is ever so slightly worse than ProRes 422 Proxy

What am I missing?