I have fought many teams where it is just the same person for the first four people and then the last one is different.
I think a simple solution to not have to fight the same person over and over would be to make it so if there are less than 5 people in the guild they can’t do guild wars.
Another solution is that each player can only cover one slot, so if there are only 2 people in their guild then the first 3 fights are free max wins.
Currently having fewer people can be very powerful versus small guilds(5-10) because they can have a super powerful team for defense all the way through, where bigger guilds are less likely to have good defense for the first few defenders.