It isn't something completely different. It is all aimed at the same thing which is making the team better and harder to beat, and creating a culture where team mates trust in each other.
If you choose to send a message about standards, you can't really pick and choose which standards or who they do and don't apply to. You can't be not good enough but its ok because its for a different reason than someone else who isn't good enough. That'd be like a work place deducting pay from anyone who turns up late because they want to see an improvement in overall performance, but then giving the extra money to people who turn up on time ad try hard but get next to feck all work done. In theory it might kick the latecomers up the backside. More likely you'll end up having to grovel back to them because no work is gettng done and then they'll tell you that they want more money regardless of turning up late because of how valuable you've just proven they are....and at the end you are right back where you started except with a large chunk of your authority gone.
You are ignoring just how utter crap Rashford has looksled this season and especially in his few outings under Amorim. So this is not just a mentality thing