I went ahead and made a google spreadsheet to show what 1xp is worth at each shield rank level.
https://docs.google.com/spreadsheets/d/ … sp=sharing
As you can see from the sheet, the ISO gained from xp gets worse and worse as you level up. This holds true until level 100 where you get a boost. I’m noticing that as I maintain a larger 4* roster, I’m gaining XP at a faster rate, which could be why they decided on diminishing returns. I wonder if this data needs to be paired with level up dates for a group of players to really see how the shield rank rewards iso per x amount of time played. I’m interested to see if anyone else has data that could further this analysis, or has anything to add or correct really.
Also this could be a good tool to help people decide if they want to champ that 
and recycle it. I know some people still don’t do that at all.