I understand why the design team would want all characters to improve as they level, but currently it makes no thematic sense on how it works.
How can the untrained sultry Cha 20 prostitute be as good at diplomacy as the legendary, but ugly Cha 10 Spymaster? My concept to fix this would be capping your bonus based on your proficiency level.
Untrained: you gain no proficiency bonus to the check
Trained: You gain your level as a proficiency bonus to the check up to 5
Expert: The cap is raised up to 10
Master: Cap is 15
Legend: Cap is 20
Each proficiency level could impart the bonus or negative it currently does also (-2,0,+1,+2,+3 respectively).
