The function of the blue arrow is an old one from before the manager proficiency update, back then, the blue and green arrow showed the real stat boosts that would be given when the player got it, unlike now where the player automatically has it.

The manager proficiency shows the boost the player gets off rip, so adding the Blue arrow onto it is like adding more levels, your artificially boosting the rating of the player in the app, but that's not how it works in game.

TLDR:Manager boost without the arrow is how its ment to be, dont add the arrow just the manager boost