NH used him more as a RWB when firstly Sanderson and then Osei-Tutu weren't able to fulfil that role successfully enough. Bacuna did well enough in the role when covering for Sanderson but was exposed when it, through injury, become a more permanent position.
Mick is now using NG as a makeshift LB cover so issue hasn't gone from the club - how do you cover all positions when having too many similar but expensive CBs and CMs? - even if solution is slightly different.
Just to extend my piece on Bacuna but when was the last time he was picked as a CM in a midfield two? He was signed as fullback/midfielder cover and you're saying he's not a fullback when the managers are saying he's not a CM in a two, the formation used here, so why did we sign him? He's a fine player in a formation we rarely if ever use.