True, wasn't thinking multi-class for once Monks current max is AC20, same as Plate+Shield without stance. Would it break things if the Monk mc'd Fighter 1 to get that bonus?
I think my DM was more worried about having to choose two longswords over longsword and dagger to be optimal in TWF stance, and L+D would be a much more common setup. This way there is a trade off, but you can choose thematically instead of mechanically with no real penalty to damage. It's not like the dagger can't ever do that damage in the hands of someone else, like a Dueling stance or even a rogue, so its feasible. For a fighter, the longsword will still have a higher maximum each hit, and it will shine more with crits/OA's, so dual wielding daggers with TWF stance is not optimal. This version of TWF benefit is still getting that d8 weapon in your primary hand.
I know you disagree though. We might have to houserule that one.