In terms of level & meter both integrated LUFS and RMS are important.
There are however a number of various dimensions relating to dynamics that need to be mastered, much more complex than you think when we consider going for specific dynamic archetypes/mix sound types.
It does not appear like that at first when you throw a limiter on the mix bus, but you will quickly realize it is so when you observe the steep performance drop above say -12 integrated LUFS. For most engineers out there (excluding those doing this at the professional level), it is a very challenging process to get to a target quality level as you are approaching closer and closer to say -7 integrated LUFS. Why, because to succeed in this you need to understand the deeper aspects part of and within the dynamic process, stuff that is really not that much discussed online but that many pro engineers are aware of to varying degree.
One of the reasons why you need a deep insight into the world of dynamics, is because dynamic archetypes/mix sound types are to some degree a product of specific monitoring environments that allow certain gain staging performance to be achieved. With extremely good monitoring you can achieve really nice dynamics. Your dynamics insights are what allow you to understand how all of this works and how to achieve the sound you want. At that point it is getting easier and easier to succeed in the maximization of those last few mix dBs.