Garvey makes is clear he wants you to take over and not do any general stuff himself as hes more of a fighter so I doubt its the case of him actually being a higher rank. Garvey cant think or strategize, ( and this is where im assuming my SS helping them would be, unless you RP a more fighter type guy ) probably resulting in the numerous people lost under his care on his way to sanctuary lol.
He's not a thinker, just a do er. Too bad he doesn't do anything rofl...
His constant quest spewing is just the mechanics keeping us busy while giving us something quest related to do every time. I think a help board or wanted board would have been a more realistic option, and they would be in every settlement. Either outside the limits or buildable like the bell, that way if you delete them or don't have it you need to manually go to places to see if they need help or the trader/supplylink type settlers can mention it like garvey does but only with the linked places.
Garvey is pretty all knowing when it comes to things happening in the wasteland.