I recommend suggesting he swap to Samurai once reaching level 50. I'm not much of a melee player, but as I've been leveling all jobs and as I finish up melee, I find that Samurai is incredibly forgiving despite how powerful it is, not to mention it's also very easy to follow even when first unlocking the job and having to sort through all your abilities from 1-50 at once. It barely needs to worry about positionals at all and doesn't even have them until you unlock the kenki gauge. Things get a little busier once you get into the 60s and 70s.

On the flipside, Dragoon's combos are fairly straightforward, but they get a pretty large list of buffs and off global abilities that have all different durations that can very easily desych. Some refresh every 30 seconds, 45 seconds, 60 seconds, 90 seconds, and 120 seconds. It's a much steeper learning curve in my opinion.