Dark Ages

In my opinion, this is already a pretty cool bonus in itself.

Well, I wouldn't say so... One small axe probably doesn't do much damage, and adding a second one will just bring it to an acceptable level. Considering that this requires sacrificing the combat training skill and the option of using a two-handed weapon, and also the theoretical possibility of holding a shield or some other item in the free hand, it's not enough.

Regarding the damage, it's not entirely clear yet. While the goblin has the same weapon in both hands, doubling the damage makes sense, but what if he later finds a suitable one-handed weapon that is better than his original one, and replaces one of his axes with it? How will it be calculated then?

I can't judge about the probabilities, as I don't know their standard values. In general, if we look at it purely logically, then they (the ones calculated when hitting an enemy) should not be increased, but simply calculated twice for one attack, but this will create additional load on you... And how are you planning to calculate the "bugs"? There should be a similar system here.

As for the AoE, yes, I agree.

and then he'll start flying on a board and throwing grenades

and then he'll meet an opponent with the "spider intuition" ability and nail himself to the wall with the board