About 50 people from Monolith Tokyo assisted on Breath of the Wild according to a 2018 Takahashi interview.You definitely have to account for how much their dedicated BotW2 support team takes up. How many staff members from MS did work on the original BotW?
For the record, Division 2 seems to be the group assisting on Zelda. The Division 2 recruitment page was the one using Zelda imagery and I doubt the new Division 1 project Takahashi's been talking about is Zelda when he had no involvement on Breath of the Wild.