The good with Harmon’s analysis is that he does a pretty good job isolating the WR and their route. So if one WR has a good QB getting them the ball or a bad QB not getting them the ball, it can account for bad stats.
Where I think RP is a bit flawed is that he basically solely looks at how a player gets open. So for example he - and a lot of people - loved Ricky Pearsall because he does run good routes. But it doesn’t really take into account that the boy is light, struggles with physicality through the catch and as a runner. It also doesn’t weigh for age where Pearsall has had 3 extra years of life to develop his route running than say Keon Coleman
So it’s a good way to tell you how good of a route runner a player is right now. But not exactly what they will become and how they are in other aspects of being a WR. In general, Harmon’s RP is very good though.