Control Reversal in WWII

In discusing the characteristics of how the Me 109K should be flown
against the P51 Mustang and P47 the issue of control reversability
came up. Would someone be able to expand on control reversability.

The Me 109 G10 and Me 109 K4 (G14 was a stopgap due to engine delays
in the G10)had a powerfull engine that allowed them to do a speed of
458mph and outclimbe all allied aircraft. However the old crate had
an old wing section that created enormous aileron forces for the
pilot; also becuase the the small Me 109 cockpit a pilot could
generate only 40lbs of joystick force could have generated 60lbs of
force in a P51. As a result only 2-3 degree of airleron deflection
was possible at 400mph the 109 had a roll rate of 45 degrees/second.
A FW190A and even a P47 could have managed nearly 180 degrees in that
time.

The issue of control reversability then came up. If power ailerons
were fited to the Me 109 they would have allowed a greater deflection
but would this have caused control reversability at some point as the
wing twisted and the ailerons acted more like trim tabs?

What causes reversability? Why is a slab elevator sometimes used?

I've also heard of WW2 pilots using trim tabs to pull out of a dive or
get an aircraft rightway up. What were they doing?

The P38 had a smaller turning circle than the Me 109 (presumably at
lower speeds of around 300mph) but its roll rate was even worse than
the 109 and this is how 109s escaped P38s and I note that some late
war P38s received power controls.