Watched the series. Great series (if I remember every-thing right as I usually try to do). There’s a-lot of fore-shadowing and things I believe (off the top) that you might not pick-up on right-away until later. And everything gets tied-up later-on in the series. I might have to rewatch the...
They weren’t good enough? They did every-thing Goku did and were at-least up-to that point I think 3 of over-all 5 who even made it to Kaio-sama’s place in the first place. Kuririn could even take the Genki-Dama in the fight against Vegeta. Goku said the Ki (or Ki-control) was too much to use...
Yamcha & Kuririn & Ten-Shin-Han
I know people ask about the Kaio-Ken & it might be valid but this is even more important, if they had Genki-Dama they could have thrown it at Mecha-Freeza when he came to the earth (maybe not considering Vegeta was able to take a less than half-power Genki-Dama...
Also Kimetsu no Yaiba. The art is rather basic in the manga, where-as it's very very elaborate to the point they look rather different out-side of the big page spreads, but then again even those are so well animated that you can barely keep-up in the anime (when it's moving).