I guess it's worth talking about "difficulty" with respect to bore size... There are multiple dimensions to it - I've almost always found larger bores (and larger mouthpieces) immediately easier to play, there's a larger target (a less rigid slot) for each note which allows for things to be easily played without chipping notes and so on.... But this comes at the expense of efficiency and endurance. But this all sits on a spectrum - so it becomes a balancing act... You wouldn't give up all your playability for endurance, or all your endurance for playability... So you look for the best balance of both. Throw sound into the mix and it's not necessarily an easy decision. I'm not sure how much of this can (or should be) prescriptive - rather, it's useful knowledge and a pause for thought against rushing into the furthest extremes in either direction without careful consideration.