Personally, I believe it would be an inherently risky strategy to predominantly utilize Herrera as a no.6. People will invariably reference the game against Chelsea in 2015, as justification for why he can do a good
job as the deepest midfielder. However, they fail to acknowledge that not only did Herrera switch off allowing Hazard to score the only goal of the game, he nearly made it a second goal deficit with a deeply underwhelming pass which momentaraily put the team in jeopardy. Moreover, they also fail to acknowledge that it wasn't the only game Herrera played as a DM under LVG. Indeed, Herrera was also utilized as a DM against West Brom in May. a game which we lost 1-0. More pertinently, Herrera didn't have the same galvanizing influence as Carrick, which meant West Brom were successful in there tactic to cede the majority of possession, congest space in a resolute defensive display.
I felt Herrera's best performances for us, were doing that spell following our loss against Arsenal in the Fa Cup, until Carrick had to come off against Man City due to a calf injury. By way of illustration:
https://i.makeagif.com/media/4-15-2015/_eSAxV.gif
http://38.media.tumblr.com/050cae8042aa02dd94738e98f4007c0e/tumblr_nlnvwzO1lb1qaorn7o1_500.gif
https://media3.giphy.com/media/CQScxklmNDulq/200.gif
Even when we played 3-5-2, or a 4-4-2 diamond, he was
still one of our best players as the RCM.
Having Herrera as the RCM, Pogba as the LCM and then somebody else behind them is the best way to go imo. I said in July that Pogba flourished when Marchisio entered the fray, over Padoin. The midfield now had a player capable of being a deep lying playmaker, whilst concurrently being a grafter, as exemplified by the fact that Marchisio was one of the solid, energetic foils with dogged determination to compensate for Pirlo's defensive frailties. With Pirlo, Pogba was more of a shuttler, but looked more liberated with Marchisio and a defensive box to box in Khedira. It's noteworthy that Herrera is very tenacious.