I wrote it as the big one because its the most obvious one.
And no not everything with time travel leaves a plothole. The plothole here was left because of a forced continuation of the story, so it was just an oversight on Toriyamas part as he practically forced the story to continue. Even setting 17 and 18 aside, you still have Cell. The one android thats a bilogical creation. Besides even officially Babidi never though of encountering Goku and the others. His idea was for Yamu and Spopovich to pretty much gather the energy from who ever they came across. Going to the martial arts tournament was their idea seeing how he was surprised the brought him that much energy with no information on the location.
but u are acting as if all the events that happened in the Buu arc would happen if the androids were still alive and won. There would be no tournament for Babidi to want to go to. and cell in itself was too low for when babidi would've been looking towards earth.