A few things I see.
const JOIN = 'n.vid = nr.vid'; this is dead code. Not sure where it comes from but as far as I am aware there's nothing in
SqlBase that uses the constant
JOIN. I am not sure what this even wants to be.
Your process copies the
type and then in the
destination I think you try to set the type/bundle to article but that's simply not how this works. Everything under the destination key is passed to the destination plugin as configuration and the way we designed and implemented this system the destination plugins do not change a thing, they just import.
In your particular case, you could use a map similar to
und: en to map blog to article but if you want article nodes then you must use either the constants or the map.