Sure, a decent coder can learn to write "hello world" in any of those languages, but if you need to pick up a legacy system and understand what's wrong with it (I think this is 80% of the jobs) it takes depth. If you've got enough depth in how systems work you can get sort-of up to speed in various languages quickly, but there's no substitute for taking the time to know the details of what you're doing.
As for LOB work I can say that LOB systems can be a lot of fun to develop. Your average e-commerce or social media site is basically an LOB system. Developing a system of practices that lets you deliver LOB systems on time and under budget is a challenge, but in the right environment it can be done and there is something very satisfying about delivering something that makes people's work easier.
The trouble with LOB work is that it's usually not greenfield work when it comes to you. They had some junior guy who never heard of primary key integrity build an app in an access database and a year later the database is full of junk and the app doesn't really work.
The process of rebuilding the schema is tortuous and then you need to update every single screen and script to work with the new schema and then there's the long and involved process of reconstructing what the database contents should have been with minimum data loss.
Although maintenance programming can really widen your skills and ability to deal with "it" there's also something destructive about spending all day deeply understanding the logic of terribly flawed code.