What if the Z-Fighters found more people to help defend against the Saiyans?
The Saiyans are coming, Vegeta and Nappa. Goku is training in the afterlife for a year. Piccolo and Gohan are training in the wilderness for a year. Tien, Krillin, Yamcha, Chiatzu and Yajirobe are training on Kami's Lookout for a year.
What if the non-fighters used this time to contribute by recruiting some more candidates? There's no one out there that could defeat Vegeta and Nappa solo but maybe there's some people who could contribute as part of the ensemble. Especially if they go to Kami's Lookout to get some training.
Yajirobe is treated as a joke for most of Dragonball Z because he's so much weaker than the others and he's an uncultured glutton. But in late Dragonball he's pretty formidable, he defeats one of Piccolo's offspring and stands up to Goku so he's not a complete weakling. Next down the ladder of strength is probably Mercenary Tao and Master Shen. Easier said than done to convince them to contribute but Piccolo agreed to help too and they won't want the Saiyans to destroy the planet, that's where all their stuff is. Tao and Shen are both stronger than Chiatzu and they're not fighting alone, they only need to join in with the others.
An often overlooked fighter is Shen/Hero, Kami possessing a normal human body. He turned a mild mannered reporter into one of the strongest fighters on the planet including massive energy attacks and the power of flight. If Kami found a willing volunteer, perhaps someone who already had martial arts experience or some limited ki control they could be even more powerful. Maybe someone else from Krillin's dojo, or Nam or Pamput or Ranfan.
Master Roshi said he's too old to fight which makes sense but again he's not as useless as he looks. He kept up with Kid Goku when he was dressed as Jackie Chun. He's faster than he looks, can bulk up his muscles and rock a giant kamehameha, that puts him above Yajirobe and since the entire planet is on the line it's worth a try. On that topic, the Ox King trained with Grandpa Gohan and Roshi, he's huge and strong and knows the fundamentals of ki control.
So Bulma and Chichi gather all the new recruits outside Korin's tower. Tao Pi Pi, Master Shen, Roshi, Ox King, Nam, Pamput, Ranfan and the Orin Temple fighters. Anyone who can fly should go up to Kami's lookout and train with the B-Team. Anyone who can't fly needs to climb the tower like Kid Goku, get to Korin's house and drink the Ultra Divine Water, that should get them the power needed to finish the climb to Kami's Lookout. Then they have ~9 months left to train with Kami, Popo and the others.
Remember Krillin training with Kami took him from being kicked through a wall by Raditz to having the power to open the fight with a multi-target beam that kills three or four Saibaimen at once. How much stronger could Nam or Tao Pi Pi get with some extra training? And whoever is the weakest and unable to contribute on their own could volunteer to host Kami's spirit, with Pamput instead of a non-fighter he could be even more powerful.
The objective isn't to find someone stronger than Vegeta. The objective is to find people who collectively can contribute more than Yamcha did and not get Yamcha'd immediately. Worst case scenario, Nam or Ox King is the one the Saibaiman picks on to kamikaze, which would leave Yamcha alive for the real fight against Nappa. Piccolo and Krillin had a good plan to attack Nappa from multiple angles at once, but it failed because they relied on Gohan to be the damage dealer. But maybe Tau Pi Pi could be the damage dealer with his Super Dodonray or Master Shen or Master Roshi or both. Or when Chiatzu blows himself up to deal minimal damage to Nappa, that's when three kamehamehas hit him from all sides.
What we need is the opposite of Dragonball Z Kai. Instead of trimming the filler to focus on the Saiyans, add MORE filler and focus more on the unsung heroes from OG Dragonball.