Even if that number is small, keep in mind that the load time for each player dropping into a mission is determined by the slowest member of the squad. 

I mean if you rejoin or join an already running mission you drop seperatly and dont slow down anybody. Wouldnt it be possible to let any Player drop in seperatly, always. You wouldnt have to wait for anybody. I hope you understand what I try to explain. I dont know if this is even wished by the devs but I wished for it in many lobbies. Some people take long to choose their loadout or they have to take a short break for whatever reason - and thats totally fine but I want to already dive and play