7: The bow doesn't disintegrate, your character simply switches to their melee weapon and attacks afterwards.

8: Perhaps Barbatos lost all his recipes when the crew got shipwrecked? Alan doesn't know how to do anything, but even if he did, since he apparently just was brought to Sentinel Island right away, he probably didn't get the chance to take anything with him.

9: That's not a good reason to pick Radcliffe in my opinion, since I'd advise for doing all the flying fortresses anyway. Radcliffe only has a single quest, even if it allows you to expand the platform twice, you gain less experience that way. Plus, you have to go through the entire Orobas Fjords before you can even attempt it.

With Kenneth however, I see even less of a reason. I mostly see people advising for wizards to pick him, but the amount of experience you lose by having to give him the book called "The Demon Wars" just isn't worth it. For reference: If you have Hermosa, she only wants Kali's sword, which is pretty terrible at that point in the game anyway, so the book remains for you to read. In Ego Draconis, you gained as many as 5 skill points from it; in DKS, they made it slightly less powerful, but I think you still get 3 skill points.

Since your trainer doesn't actually increase your skill level, but only raises the maximum level possible, unless one relies on very specific skills and needs these on a high level already during Ego Draconis, I can't see how a case for Kenneth can be made. Once the player reaches Flames of Vengeance, there are further trainers in town anyway, who can train those skills your platform trainer doesn't have access to.