DGM has some conception of power levels, and they're listed in the fanbook. He's at level 4, below the Generals/Allen but at the same level as Lavi and Lenalee. In other words, yup, Kanda is definitely one of the best fighters of the Order. However, if it took Allen, Lenalee, AND Cross to defeat a level 4, I don't think it's realistic that Kanda and Allen would be able to. Kanda's at Lenalee's level, and he can't combine his power with Allen's in the same way. And even then, there's still the missing Cross.
DGM isnīt very evident when it comes to "Power levels" but personally, i think Kanda is probably one of the best fighters in the Organization and he did have a serious disadvantage for not having his innocence ready when the original level 4 attacked, fighting only with a normal japanese sword (What donīt those guy have in their warehouses). If Hosino makes it believable, i wouldnīt be too surprised if Allen and Kanda manage to kill him, especially with the Crow back up that just arrived.