I think the shorekeeper/rover buff is there to help f2p players not feel the need to skip her. If you don't have many dps then skipping shorekeeper seems appealing but she is going to be such a valuable pull for everyone's account.
personally I think it really is just there "for flavor". It's not that big of a buff that it feels bad to not have, but its enough for players to appreciate that Kuro is willing to showcase the in-lore connection of SK with Rover through extra buffs in gameplay. Same as with Dreamless echo being buffed by Havoc Rover's Ult
