There's two flaws to your argument.
1 - Jamie Murphy was a more rounded player and had to play in league 1 for 2 seasons in order to develop for the championship.
2 - marvins a known quantity in England - only at conference level though.
Aberdeen are in the spfl league title race with a squad that are predominantly English league 1 rejects. Johnson was (and still is)'only proven at conference level down south. Hearts signed wigans (league one) most unpopular player / booboy who walked straight in to their team. I think Johnson has the attributes to be a really good player but don't understimate the quality and depth down south.
I was speaking to an ex player who still has ties at an English championship team and they were raving about him suggesting that they would be sending their Scottish scout to monitor him. I'm not convinced he's good enough for the championship but they are watching him that's for sure
Everyone of the players should be applauded for the effort they put in. I thought we were short in quality in the middle of the park but the 3 midfielders worked tirelessly and knew when to foul and when not to. Moult and Ripley excellent and big McManus and Kennedy came to the fore when Aberdeen started their hoofball with about 10mkns to go
I don't see the issue, we seen the game out comfortably and maybe he felt the two you mentioned needed the full 90ninutes to maintain game sharpness levels. Plus the two potential replacements you refer to are not known for their defensive capabilities.
It's hard to disagree with a lot of that. However I would query why, when we have an aging squad and we are regularly conceding last minute goals, did we sign two players who look incapable of being able to play 90minutes