I changed the heading for Column D to "Percentile" and here's my final formula:
=(1-(IF(ISNUMBER(C2),SUMPRODUCT(--([Level]=B2),--([Score]>C2),--ISNUMBER([Score]))+1,"")/COUNTIFS([Level],B2,[Score],"<>"&"",[Score],">"&-1)))*100
Would love to hear if anyone has a different approach!