Last month alone, Frogg made 6,000 kills. In the same time frame, 43,000 Engineers were able to make 110,000 kills. Of those Engineers, the highest kill count belongs to Gamemaster, with 300. His K/D is roughly 1, Frogg's is around 4.
Please explain how a single Engineer can hope to reach 6,000 kills in 28 days. Going to a different server where Sentries are more than mild annoyances doesn't count because the stats only track the OCR servers.