I've never seen any notable difference in group sizes, either.
I have not either.
I'm not much of a target shooter and didn't even know benchrest shooters primarily used FB bullets till I started this thread.
Years ago my Dad used to shoot 1/2 in groups with his Douglas barreled custom 1909 Mauser .25-06 and he used exclusively BT back then.
Maybe there is nothing to it and it's all circumstantial.
Perhaps if there really is something to it the secret might lie in the structural diffrences of BT and FB.
As far as DRT goes last year my Dad dropped one in it's tracks with his Tenpoint crossbow so maybe you never can tell.