Do you have Optimize Storage turned on for Photos on your Mac. That might explain the delay.
When I put them side by side, the pictures look a bit different on my iPhone, my iPad, and my Mac. This may be because the screens are different sizes and materials--I bought them on different years. The brightness settings make a difference, as well.
But I have to say that pictures look best on my MacBook-- better than on the iPad which looks better than my phone. But the differences are pretty small, and I hadn't noticed until I put them side by side. My MacBook is the newest. Also, in Settings>Displays I have True Tone turned on. You can try different "preset" settings in Displays-- it might be on the wrong display, or you might like other settings better.
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