your pdif averages are definitely incorrect for the first two - the function distribution is non-normal. (it's not even close to normal) mode is 1.0 when 1.0 is in the range; this has an effect of inflating or suppressing pdif_average by a significant margin depending on whether 1.0 is above or below pdif_mid. your pdif_average above 605 is possibly correct but not provably so without extensive testing that none of us has been willing to do yet. (pdif_average = pdif_median = pdif_mid is only true for certain possible distributions and not for all of them.)
the pdif_max under crit is in excess of 3.0
[1]
this is true as of the end of the 2h buff/nerf (the one that made sam ws weaker and changed boost from str/dex from 1:1 to 4:3) so it should still currently be true. (this is for both 1h and 2h weapons, although I linked kirschy's post because it's about 2h specifically. see the OP for the 1h/h2h version.)
any mage with both dia2 and erase should be casting it on birds btw. yell at them if they aren't.
anyway, the basic evaluation you made is pretty accurate, with bad attack ratios crits and double attacks become pretty close in overall damage increases.