Is it necessary to have 2 heroes per castle?

I remember a long time ago, back in the third installment of Heroes of Might and Magic, my friends and I would discuss the game's conditions beforehand – no holding down the "S" key during battles, no leveling up Diplomacy, and limiting ourselves to only 2-3 heroes for the entire game. Later, I saw "experienced players" in a club playing, and to my horror, they had a huge number of heroes! At the time, it seemed like a silly idea – it's inconvenient to control so many, it costs a fortune to maintain them, and there's simply no need for so many, they just get in the way. The third and fifth games have a lot in common – if you play for fun, to enjoy yourself, and develop a powerful hero, you can play with just one. But without a group of heroes, without chains of movement across the map, it's impossible to win against a skilled opponent who can perform more actions in a single turn than you can in a week.