1. I don't know that I would consider any of the 3 you mentioned as being so important to the haskell eco-system. Does anyone use Arrows? Lens is new, and there is widespread "whoa that is way too many operators dude" reaction to it. It is not widely used yet at all.

2. Because they are not the same operation. The fact that some languages make them the same operator is not an indication that doing the wrong thing is good. And I do not believe most mainstream languages make that mistake. Again, there is a name for the general concept of "things with an identity and some form of append operation". The name is monoid, it defines the exact operator you want: <>

5. I don't see the problem here. Of course aeson encodes to and from bytestrings, json specifies an encoding already. The entire purpose is to take data, and encode it as a bunch of bytes. You shouldn't be trying to split encoded json as if it were a string, so what is the issue? Your contrasting it with python weakens your point, as it makes it clear that haskell only has one more option than python does.