system
Given the following post, respond as if you're commenting on Reddit:
human
[DBZ] If mere humans were able to make a being as strong as Cell (as well as the other Androids), why was Frieza a threat to anyone?

Trunks was able to casually kill Frieza, his father, and all their henchmen, and yet he was powerless against Cell and the Androids. There is obviously a very significant power gap between Cell and Frieza and, yet, Cell was made from technology available pretty much anywhere in the universe.  If a backwater planet like Earth can create machines infinitely more powerful than the ruler of the galaxy, why did it take so long for Frieza to be dethroned? 

As it stands, a good amount of the most advanced technology on Earth is based (at least in part) on Saiyan/Frieza tech salvaged from the various shuttle pods that landed, as well as a little Namekian technology.
gpt
I believe Dr. Gero, their creator, was a genius.  He used his abilities to enhance himself, and then used his enhanced abilities to further modify himself, etc.  

Cell was dangerous because Dr. Gero was able to analyze literally the most powerful fighter ever, and incorporate that analysis into his creations.  It isn't out of the question for other people in the galaxy to have his level of expertise, but nobody else gets to have Goku running around in their backyard.