In my opinion, the design is much better than preceding SE 2020, X etc. It is much easer to hold and use one-handed 80% of the time. The other 20% I use reachability when needed.
Upgraded from a xs max to 12 pro max, use to find the xs max slippery to hold without a case, the 12 pro max has way more grip when holding the phone, the flat edges definitely adds more grip.
I have a 12 mini, so I'll just speak to the shape rather than the size since obviously with the 12 mini reaching and all that isn't an issue. I prefer the flat sides that the 12 has than other models. It really does feel better in your hands. There is just more surface area to hold onto without making the phone bulky at all.