There can be no doubt that the much more lightly loaded 109s would be superior in a sustained turn than a 190, BUT, one wonders if our A-5 should turn better than it does. The wingloading is not all that different from that of a P-47 D-11.
A5 has better turn rate but larger turn radius than the D11 from the stats I have.
Also, I know what you're talking about - all the stories that the 190 totally outclassed available Allied fighters at the time.
To really assess this claim, you have to consider what its contemporaries were. What exactly were they?
Going off the fact that the 190A5 shows up in the EW perked, its European contemporaries were Spit9 (also perked), P40E (not sure on this one), and P38G.
The 190A5 is as fast or faster than all of them below around 25k. It outclimbs all of them except Spit9 (it outclimbs Spit9 down low but loses advantage above 7k). Its turn rate is competitive with all of them (one or two dps for 40E and 38G, 2-3 dps vs Spit9), though its radius is lacking.
Oh right it also outrolls all of them (horribly, it's not even close) and comes with the option for a 4x20mm gun package.
So when it was new, the A5 was faster than everybody else, could pull its nose in position just as well (though could not sustained turn as well) as anyone, and it could out roll everybody. Oh, and if it got you in its sights, you were pretty much dead because of its massive guns package.
I think that puts it in context better. I also do wonder if it turns better; I love flying 190s and definitely wouldn't mind if they turned better, but given my analysis and the fact that historical anecdotes are subjective and based on incomplete information, I think what we have modeled is reasonable.