Right, calling it technically lossless is wrong but 422 HQ gives impressive results so I we can probably safely say that it is "practically" lossless.
In DaVinci Resolve, many tools go awry with image sequences: for example temporal noise reduction simply doesn't work with a compound clip with image sequences, I also remember having problems with caching performance. I have a few very strange/buggy problems with Resolve though I love color grading with it regardless, so I want to avoid the buggy sides of Resolve (as it's one of the buggiest software I've ever used) but use the upsides of it (grading and some OpenFX filters).
Ffmpeg can encode into ProRes, but it’s technically an unofficial implementation.
What issues do you run into with image sequences?