IMO, how well are the M/K vs gamepad controls are totally subjective. The OP brought up DAI and even among M/K users, there are mixed feedback. Generally, those who are use to GW2 MMO action style M/K controls will feel right at home.
I have played M/K and gamepad for both DAI and TW2. I can be drunk and half awake and still faceroll most enemies on Dark difficulty in TW2 and Nightmare in DAI using a M/K. However, even fully awake I still get my behind handed to me when using my gamepad. I am sure gamepad experts will tell me that I sux with a gamepad and I believe I do but the same can be said about those who cant get use to the M/K controls.
p/s: If DAI is designed for gamepad, it is done even worse than M/K. You cant even rebind buttons.