The top models always lose more value than the base models. Part of it is Apple's huge markups not translating to what it's actually worth, and part of it is people who want high-end machines (rather than the bare minimum at a good price) already set on going for the latest and greatest.
Absolute $ value will be a bit higher still on the M4 Pro but far less % of the value retained compared to the M4 (meaning they'll be much closer in price).
This is so true. In November 2021, I paid over US$ 3,100 for my 14-inch M1 Max MacBook Pro with the 512 SSD, 32GB of RAM, and the 24 core GPU. When I decided to move to an M4 Pro mini + MacBook Air combination, I sold my MBP for just over $1,400.
I ended up selling it for over $1,700 less than I paid for it. In my area, I saw similar MBPs but with the M1 Pro sell for just under what I sold mine for, meaning the M1 Max was not getting that much of a premium over the M1 Pro.
Over the three years I had it, I never ended up using the M1 Max to its fullest, and the M4 Pro mini is perfect for my needs. This time, I decided against speccing it up and just got the base model M4 Pro mini and combined with a 4TB external SSD I haven't noticed any difference compared to my old MBP (the mini is faster in a lot of tasks).
What I've found with this experience is I've previously purchased more than I needed, and for me I will do minimal upgrades for future Mac purchases (probably only RAM if I feel it's needed for my main machine).