No Sephiroth clones received stronger doeses of Jenova cells and mako energy than did the normal members of SOLDIER. The Sephiroth clones were the dudes in the tanks at the Nible reactor (among others that came later on i would assume). Normal SOLDIER people only get showered in mako, Seph clones are emersed in mako and kept there for extended periods of time. That is why Zack, a normal SOLDIER, lost to Seph so easily.

i believe that the only thing the Jenova cells did was immediately make Cloud stronger by making his body become stronger and so when the j cells left it didnt matter because even though the j cells had caused his body to become stronger they were not needed to sustain his strength, in other words the j cells had been the catalyst for Cloud's own body to make itself stronger.