Slow loading and bad thumbnails with HEIC in Photos

I have started to export and transcode my full frame photos in Lightroom to the HEIC format. Mainly to save space in the Photos library. But also because I believe that this is the format for the future.

What saddens me is that the heic-tumbnails in Photos app are so poor. They look like something from the past. With color fringing and visible pixels. Also going full size with the image, Photos app uses 3-7 seconds to load the image properly. JPGs in the same resolution loads in half a second. This is really messing up the experience of the Photos library.

Photos taken with the iPhone are also in the heic-format. But the thumbnails are crisp as winter crystals. I believe that iOS photos are optimized by Apple somehow, but phone photos are also three quarter the resolution. I know that heic is a harder codec that takes more time to unpack. But still.

So my question. Are anyone else experiencing the same problems with thumbnails and loading times on heic-images that have been transcoded from high resolution jpgs?

I have the same thumbnail and loading issues with the Photos app on both my MacBook Pro and my iPhone 14 Pro. So this is an macOS and iOS universal issue.