Saying you have been disconnected by the host makes it sound like the host did it on purpose though. Which I can still guarantee that 75% of the time that still is not the case. Since most people are in some strong belief that all lobbies where you disconnect from are doing these things on purpose, without thinking about it in a more technical standpoint.

It could be your own connection to the host or the hosts connection to you was bad in general. It probably had to take something like starting a game, or fighting a very lag inducing event like fighting a boss for the bad connection to kick in especially if that person has a lower end device in general. I doubt most people would wait to disconnect at the very end of the match just so they can prevent a loss. If that were the case they would have disconnected the players right at the beginning, as why would they wait til the boss fight to disconnect when if they're planning on doing this on their own anyway they won't have any reason to take you up to the point of the boss before disconnecting since waiting for load times is just a waste of time. Even then most of my own disconnects when I host happen at the beginning as I don't play any raids in Multiplayer with large bosses like Manda, Susanoo, and 9-Tails. It's common for people to disconnect at the very beginning and for something that is not your fault.