I did my first full run with the 5-members party, but after trying 4 I think that for me managing 4 is optimal.
There is a huge growth in buttons, controls and overall micro, especially for multiclasses, and on high levels my control panels start to look like some airplane cabin.
I was against party size restriction, but now I see that it makes sense.
All my future parties will be 4.
I agree that there are a lot of buttons, but it is NOT that difficult to manage a party of 5. Just make sure that most of the party has their AI engaged and you can let them go. The AI in POE2 is solid, and thus far, it appears to me that AI controlled party members don't do stupid stuff.