May also be a programming thing... That Gero made Cell in a way he wouldn't rest until he reached that ultimate power... And maybe the concept of the goal for reaching perfection Cell was programmed to have as a goal had Saiyans cells such as Vegeta and maybe Freeza specially shine brighter due to their obsession with power and the overall 100% certainty they can't be defeated. I think Cell also wanted a good challenge, he'd find it boring being the strongest without anyone to test this power against, then I think maybe Freeza's cells standing out were replaced more by the Saiyans desire to test that power, mainly Vegeta's and Goku's, with the CGs... Still though, more like having a Vegeta's perspective shining brighter. Maybe though, narratively it contrasted a little nicely with #16 noticing he had no opponents and then bam --- someone stronger than him showing up. Or maybe it alludes as well to Gero's and Cell's greedy for power with the theme of constantly wanting the ultimate, the super ultra non-stop relentless pursuit of this thing, this obsession, which seems to be a theme too, with how for example, the SSJ was this invincible thing and Vegeta couldn't believe when it was surpassed and thought of something Trunks never thought and didn't even think as possible --- surpassing what was seen as the pinnacle of power. This perfection thing may just be the thing he wants to put to rest any possibilities. Freeza for instance had some fears of a potential Saiyan be developing himself and becoming a thread to him, like a premonition, which Zarbon kinda, tho not openly stated, found nonsensical... But the lengths he went to, calling the Ginyu Force to deal with Vegeta... And I think even wanting to have eternal life, may have been a response to this uneasy fear, which didn't have for Freeza any tangible evidence and even though it was in fact happening, speaks a lot about his overall fear and cautiousness too. So I think Semi Cell was kinda sharing that side at the time... Not pushing his luck at any time.
