First time posting here so cut me some slack if I screw up. Simply put, if the game mode isn’t ranked, there shouldn’t be a penalty for leaving. Me and who ever else is playing in a match, doesn’t want to see a warlord have to chase down a shinobi who doesn’t want to fight for the entire round and likely the game. It’s not like it’s even practical, you can just make your console or pc go offline for a second and get disconnected penalty free. This “feature” just harms people who want to play the game from what I’ve seen.
When players are able to leave freely, it also harms the people left in the game unfortunately. There was a fairly recent period where the penalty was not in the game, and the amount of people reporting bots filling up their matches was quite high.
There's pros and cons to both ways, but ultimately I think we'd rather have as many quality matches between humans as possible.