I just recently went back to the Pro Max, after going Pro -> Mini in previous cycles. Overall, the Mini is far and away the perfect iPhone form factor IMO, minus one thing - battery. I would have stuck to the mini, but the lack of "pro" features (Mainly 120hz) and lack of battery forced me away.
For me, the Pro size is already compromised, it is too big to use with one hand comfortably (Comfortably being the key - I can use the pro max with one hand by doing some shifting around - but it is the same shifting I have to do to reach the top corners and the keyboard at the same time on the Pro.) So my logic from that point is that the Max has a bigger display and longer battery, so why compromise on the "medium" sized phone that is already too large, just go with the largest option.
The Max still annoys me on the software side though, basically nothing actually takes advantage of the larger display. And basically no apps support landscape mode anymore (With two column layouts.)