but more power should allow you to be slower still
A little bit, yes.... To reduce turn radius... not really. Yes, you can drag in on a wings level approach, and more power will allow you to fly a little slower, to a point. But, the same technique won't work well in a tight turn, as torque will become a factor, and handling will become terrible. You'll be so close to a stall, that any disturbance will cause a stall, and perhaps a roll off. There's enough asymmetry already in a tight turn, that adding more power makes it much worse.
Transport Canada had me flying aggravated stalls in a Cessna Grand Caravan last December: 30* bank power off stalls, then 30* bank at 75% power in both directions, then again, 30* bank at 75% power one ball out, in both directions. The addition of power degraded control, one ball out, more so. And the stall/spin entry was quite different left and right entry. I sure was impressed with the Caravan's tolerance to spinning though! (And I passed the flight tests!).
During towed "bird" flight testing I did in another Grand Caravan many years ago, I found that the P factor was really upsetting the winch recovery of the bird, and often I would glide the plane, and occasionally feather the prop for bird recovery, as then the airflow around the plane was very symmetrical around the plane.
I did spin testing for an engine change in a Lake Amphibian many years ago, and found that spins entered at 75% power either refused to enter (against torque), or simply snap rolled (with torque). It only requires one torque induced snap roll in a Lake Amphibian to tell you that you should not keep doing it! But, even with only 210 HP, torque was a huge factor at very slow speeds.
I agree that WWII propeller powered fighters might have differing handling, which perhaps would not be compliant to today's certification standards, and probably the experience base for the WWII types is small.