I think that is correct.
It is easy to say that a youngster has earned his chance, but there is no point in putting him into a team where the player in front of him leaves him exposed, as you rightly say, Lennon would have been the ideal tutor for him.
We should remember that Seamus spent some time as right winger before he became a fully fledged right back.
In fact, I think that is the major flaw with Del, he doesn't have the stamina to get forward and also get back to help out his full back in the 100 mph league that is the premiership.