It's always been hinted that Ki needs some degree of focus to be affective as a force field.
This isn't going to be based on that headcanon lore video is it.
It's never been hinted to be that kind of force field, it was always treated as something that, alongside actively concentrating it to do stuff like blasts or flying, gives passive buffs to speed, strength and resilience simply by someone having more of it. Hence Goku as a kid brushing off being shot in the head on like page 4 and him being able to throw cars around, when he didn't even know what ki was let alone how to use it.
There are inconsistencies, Toriyama wasn't overthinking the concept and how it interacts with everything else, nor was he overly rigid about it, but the general rule is that it's a multiplier to physical attributes depending on how much ki the person possesses.
That's why Vegeta got BTFO twice with a regular old samurai sword in the Sayian Saga. First time Yajirobe caught him off guard, the second time was when he was so weak he could barely defend himself.. Its why Goku got hurt by a rock Krillin threw, because he was asleep.
Swords have some strange logic going on, where they are functionally as strong as the wielder. Trunks cut Frieza into pieces with his sword, then gave it to King Cold, who couldn't do shit with it against Trunks. Both of them were a lot weaker than him. Goku is able to hold it off with just a finger when him and Trunks are about even. Then it gets busted fighting an opponent that's significantly stronger than Trunks. It's
never said or implied by anyone that the user's ki gets channeled through the weapon, but that's how it behaves.
Yajirobe and his sword would be a similar deal. People can still get caught off guard and hurt by people or attacks that are powerful enough relative to them, eg Goku getting hurt by Piccolo at their tournament fight. At that point Yajirobe'd be as strong as any of the other fighters that trained with Kami, so you could reasonably bullshit the second attack on Vegeta as being within range to hurt him if caught off guard. Vegeta ate a lot of shit by that point and was weakened a lot, and the slash really didn't do much damage.
The tail cut on the other hand is an inconsistency for the sake of story. The weak spot on the giant monster gets exploited by the heroes. It's basically a callback to when Yamcha cut Goku's tail off. In both cases, the person delivering the attack should be way too underpowered to harm an oozaru if Toriyama was anal about relative strength, but the plot has the tail be susceptible to cutting for the underdog to have an out. Hell, because it was already done once, Toriyama had precedent to do it again. It works fine narratively.
It does boil down to how much Toriyama wanted to have a cool moment or a plot point about sth getting cut at any given time. Destructo disc is the ultimate example of this. Shit's just a spinning ki blast in the shape of a saw blade, why would it be disproportionately effective against way stronger opponents like Nappa or Frieza? 'Cus it's cool. Why doesn't it get used more if it's so effective? Well, because, y'know. It was only meant to be effective in that moment of cool, not an actual way to achieve victory.
The rock thing is filler, and it's retarded that it became a go to argument in favor of this shit.
Furry-in-denial Plague of Gripes gives the best explanation of DB's power system (and why Toriyama never really went into detail about it, cause even he knows how bullshit it is).
Knew it.
I forgot how embarrassingly tryhard multiverse got.
The tryhardness is a refreshing amount of effort now that Super lowered the bar to crayonbox palette swaps.
