I'd say a Resolution Mechanic would be the smallest systemic "micro-kernel" worth discussing about a WIP game, and you don't have that yet.
Based on what you do have so far, here's some issues I see:
- Level seems much more important than Rank. Example: Rank 4 Level 20 will beat a Rank 5 Level 1 literally 99% of the time. This seems odd since I think the expectation would be Rank 5 should generally be better than Rank 4, regardless of Level. (Not sure how Ranks and Levels are increased, but didn't the 5.1 have to be 4.20 first? And now they're worse than 4.20?)
- Two equal Ranks both with Levels in the > 10 range will do nothing but tie the majority of the time, including 100% of the time if both are Level 20.
- Re-rolls are not fun, and would slow gameplay, especially if ties are common. Also, per point 2, they might be infinite, or at the very least, a single check might require many, many rerolls.
- A difference of 3 or 4 Ranks (depending on Level) means the higher level has a 100% success rate. Sounds like that's a design goal, but really doesn't feel right to me.