The machine is new enough the thermal paste is fine. I waited 3-4 years with my Latitude because it was at the point I noticed excessive temperatures and throttling. It doesn’t make sense until the thermal paste is a legitimate concern after a few years.
It doesn’t always help the temperature of the system as much as you think, but sometimes you need to do it because of the age of the original paste. High quality paste (Artic MX-4 in my case) didn’t fix the higher then comfortable temperatures on my computer entirely (partially because the MQ processors overload the cooler) - but I know it’s done on machines like that.
There’s no need to do it until the machine has older and the factory paste has dried out. Your rMBP isn’t at that point yet.