All toons should be farmable similar to the cantina table. Happy customers are paying customers. Unhappy customers are the ones that realize that it takes a large cash investment, a long period of time, and animal sacrifices to RNGezus. Those are the people who either quit or realize that it's not worth investing any money in the game.
I have not noticed any change in shard drop rate after refreshes, and I'm currently refreshing both Anakin JK nodes and Rey's node. Some days I get lucky; others I don't. I highly doubt there's a difference in code the closer you get to unlock. However, even if there is you won't get anyone at CG to admit it as they know how unethical that would be.
TLDR: It's doubtful there's any purposeful change in shard drop rate. I hear RNGeezus likes cats.
