The World's Strongest plot hole?

[Cootie]

Normally I give Dragon Ball Z the benefit of the doubt when it comes to plot holes because the show isn't supposed to be taken that seriously. But, this one plot hole just can't be ignored. Dr. Wheelo and his assistant Dr. Kochin need the strongest body in the world to put Wheelo's brain into. They remember that before they were frozen that Roshi was the strongest man in the world, but once he is captured they are disappointed in his power.

Later it is revealed that they have had Piccolo under control since the beginning of the film. Now, if they had someone of Piccolo's strength already available to them why did they bother with Master Roshi? Surely they realized that Piccolo had powers that Roshi did not posses. Also, how did they know Piccolo by name when they had never heard of Goku? They were still trapped in ice when the Demon King Piccolo re-emerged so they couldn't be it.

[Zephyr]

They seemed so mystified by Roshi's legendary status that they probably thought he would put Piccolo to shame.

As for them knowing of Piccolo, it probably wouldn't be too much of a stretch for them to have been around during/heard stories about Daimao's initial rampage.

[Gyt Kaliba]

That's what I always assumed as well, was that they just assumed that Roshi would put anyone else to shame, no matter what they found out Piccolo was capable of. Kind of like how everyone in the human populace took Mr. Satan's strength at face value too.

As far as him knowing Piccolo's name goes...at what point do they first mention his name? Maybe they just got his name after he was under their control. They probably read his brain or something, with the golden vein thing that they had on him to control him. That's not too outlandish really.

[Godo]

Also, they didn't test Piccolo's powers out like they did with the rest. He was caught in a surprise attack and was heavily outnumbered. Maybe that's why they didn't think of using Piccolo's body.
And yeah, even if they knew that Piccolo was strong, Roshi's legendary status may have blinded them. Maybe they thought of him as stronger than even Piccolo.