The aerodynamic loads are due to aileron design considerations, airspeed load, and fulcrum. The pilot, in such a small space as a Bf 109 cockpit, sould only supply so much side force for roll. It wasn't enough to give decent roll response above 350 mph or so, at least in the Bf 109 ...
and the later models were considerably faster than that, so your statement above doesn't hold up, according to history.
German tests done on a well worn 109F in late 1944 (it should be considered the 109G had more rigid, reinforced wings, so wing flexing would be less noticable) show that the aircraft could have a maximum stick deflection with 30 kg stick force, and still possess have it's peak ca.80-90 degrees/sec roll rate at ca 625 km/h TAS at 3 km altitude. That's about the maximum TAS possible for the fastest 109 variant, the K at this altitude.
Again, this is with an old F version with less stiffer wings, and no Flettner tabs on the ailerons as was done on many 109Gs. At higher altitudes, the roll rate is higher, and the stick forces are less - this is generally true for all planes.
As for the Fw 190, the fulcrum, aerodynamic design, or cockpit leverage position were enough better to compensate.
Again the FW 190 had exactly the same stick and exactly the same leverage on the stick.
Sorry, but late war Me 109 designs did NOT correct the roll problems, Fletner tabs notwithstanding. It was then and remains now a bad roller at high speeds.
This is your opinion. German testing shows the ailerons Flettners made it 2/3 aileron deflection possible at .70+ Mach speeds.
So, the Spitfire was better than the Bf 109 when rolling at higher speeds, was always equal ro better at turn rate, and remained that way until the end of the series.
Early Spitfires were definietely not, even British testing shows they can't compete at 200 mph, and at 400 mph they can achieve about the same roll rate, albeit with far greater stickforce required.
Later Spitfires are hard to judge, because no full test flight of roll rate of serial production Spitfires seem to exist. British testing, comparing Spitfire roll rate to the Mustang however shows 72 lbs stickforce is required to achieve a steady 45 degree roll rate a 400 mph IAS. The NACA concluded that 40 lbs is the maximum possible, and with that force, full stick deflection was possible up to 140 mph IAS.
However, Dave Southwood who both the original Bf 109G and (elliptic wing ) Spitfires says the roll rate of the two types is very similiar, and I believe he is probably right. High speed roll rate was not a forte of either types, but it seems it was generally OK if a bit stiff up the their level flight Vmax.
The history I have read by William Green, Eric Brown, and many other says the Bf / Me 109's were great airplanes, but were NEVER fast rollers at high speeds, and none mentions any significant improvements in my references. In fact, they all state quite categorically that the Bf / Me 109 was traveling in a straight line when over 400 mph and there was nothing the pilot could do about it except slow down and turn ... if he was able to do so, that is.
If think it says more about your references than the 109. There were definiete improvements.
Vertical dives are NOT conducive to slowing down, and many went into the ground at high speed in dives.
As did other planes.