I have always been under the impression that Tesio was more of an earner and Clemenza was more the muscle. It was Clemenza who first got Vito mixed up in crime by giving him the guns. It seems like when there is a job to be done which involves violent force of some kind it goes to clemenzas and his people. I am sure they both earn substantial amounts of money and they probably both do assassinations.(Tesio's men hit Bruno, but we know that at that time the family was still unsure whether or not Ckemenza had betrayed them.) It just seems as if Tessio was more of a business man and Clemenza a thug.