To me, a huge problem is a lack of story arc, so some initially cool character backgrounds were hardly touched upon, and "goal" for them to grow. Writers also forgot past episodes, and never used "flashbacks" as not only a creative way for a clip show, but also to show how the character "realisitically" grew.
So C.E. Evans mentioned Mayweather's original conception. He would have still worked as a young Ensign, but then show him more knowledgeable, such as treating a certain alien in a way THEY would be accustomed too (as opposed to T
Pol's Vulcan logic) or tricking a crew member into eating a certain alien dish.
On the other hand..Ensign Kim should have had a promotion (and that being a huge part of the episode)/ He could have also coached the Borg kids...treating them like he would have liked as a new Ensign.
To me...it's the writing and lack of character vision by the showrunners.