I agree, but they've made a rod for their own back by rescinding the Morelos red card at the start of the season. I've found the uproar from the rangers fans hilarious, given they've been provided so much leniency from the SFA / referees. I don't disagree with any of your second paragraph though, it does seem peculiar. Almost that they realise they've made mistakes previously and are now making them look consistently wrong. Calls for VAR to be introduced, i'm not sure the Scottish officials are competent enough to use it correctly.
Will say this though, McGregor's was a clear assault (he's done it a number of times this season). He's not protecting himself, he's out the injure Ferguson. Had the correct decision been made, he'd have been off, we'd have scored a penalty, and I doubt you'd have won. There is no reason as to why either linesman couldn't have made that call. It was right in his line of sight. I'll give Ibrox ST holder Madden the benefit of the doubt in this instance ;)