Idk just curious because in sword the last gym leader only uses 4 but hes the last one so you would think he would have 6 right?
Nope.
The closest they get are 5 Pokemon during the main story, and they're usually the last leaders.
In rematches, some of them do get full teams.
cough cough Blue has 6 Pokemon in hgss commented 3 minutes ago by GmaxStonjourner