Where do you run in to this? I switched from Chrome to Safari about 5 years ago and can count the number of websites I’ve had issues with on one hand, I think.
Mobile Reddit is awful on Safari, but it speaks more about Reddit developers than it speaks about Safari.
Strava is an example of a website that's dog slow on Safari. Pages take 10+ seconds before they start rendering.
Interestingly gmail suddenly started loading dog slow in Safari for me. I'm on an older version of Safari so that could be a factor - so bizarre though. I wouldn't put it past them to be doing that deliberately.