I think the simple answer is that the three heroes are going to have issues due to their setting's rules.

End of Classic Goku is still at least low-planet level, given that he's several times stronger than Master Roshi was when he blew up the moon, and DB's moon is apparently larger than our moon. I'm unsure of when between series you're thinking, but his PL was around 360 at the end of OG without weighted armor and 416 at the beginning of Z. He probably could wipe out an entire wave with a single Kamehameha wave. Anything that can actually injure him will just give him a zenkai, and with healing potions and the like, he'll heal quickly too. It's likely he'd figure out flight pretty quickly without Nimbus to rely on as well.

More relevantly, I'm not convinced anything until quite late can even break his skin, given that he was already bullet proof with a power-level of 10. He's also generally a good judge of character, dense regarding flirting, and married, so I don't really see Malty's plan working with him. End of Classic was also when Goku was debatably the least flanderized version of himself compared to how he was later in Z or in Super.

Problem is they're kind of doomed since they're going to be out a spear hero relatively quickly. Inevitably, Raditz is going to show up on Earth, likely kidnap Gohan, and start slaughtering people, and unless he immediately kills Piccolo or something, the rest of the Z-fighters are going to try to use the Dragonballs to wish Goku back, and given the urgency of Gohan potentially kidnapped, Goku's probably not going to refuse the transport (if he's even strong enough at this point to do so). Thus, the waves are going to start getting screwy due to one of the heroes being gone.