And lose a few elite soldiers and a wife in a process...
Yeah, and? I'd rather have that feature and lose the soldiers then not have it. It is fun.
If one of the core mechanics, the ability to save the lord (the most important asset of any kingdom by the way) in a SANDBOX GAME is made for, as you say "dumb fun", than this sandbox has a problem. It's not some Call of Duty, when you are given to ride a tank just for fun.
No, it isn't whatsoever. The ability to break your lords out of jail is meant to be fun. The entire game is meant to be fun. And I don't get why a feature being made for dumb fun makes a problem for a Sandbox. Sandbox games can thrive off of a little dumb fun here and there. And I don't think that these features were added just to be dumb fun. I also said that a lot can be added for immersion sake or dumb fun, not that these features were dumb fun.
And there is no one, definitive, good Sandbox experience. And not every aspect of the game should majorly influence another aspect of a game. Obviously, freeing just one lord isn't going to change the tides of a war. If you think that should, that's wrong. That is
one lord. It is your choice if you want to break him out or not, the game isn't forcing you. It is a Sandbox, you can do it if you like.
That doesn't mean that the other issues with Bannerlord don't exist, but the issues that you pointed out don't have to deal with Bannerlord being a bad Sandbox. As a Sandbox, BL is pretty good. Not great, it obviously has issues, but not bad. There are aspects of the game, like Criminal Enterprise, which have been criminally underdeveloped and basically aren't in the game. The problems that you pointed out deal with the fact that BL is a bad Kingdom management game, something more akin to EU4 or CK3. And I agree with that sentiment. Being a King feels... weak.