I get your points and respect your reasoning and decisions. As far as blow one's racket away, i think that doesn't apply to all situations. I mean if tanishi or Kite did a big bang on Duke, i dont the racket will " AUTO" be blown away. it just blown away on comparative weak strength ed people like echizen.
I mean didn't kite use big bang on tezuka in quarter finals nationals? it didn't blow racket away. I'm just saying you are using the BIgbang's supposedly blown racket away to reason the Muga's inabiliity to copy strength , which blowing the racket away is not a good example to prove your point imo
Tezuka returned the Big Bang with a tech (Hyakuren) which seems to imply if he didn't use a tech, then he'd have got his racket blown away. Or he could have just done it to be cool, but Tezuka never strikes me as someone who does something just for the sake of being cool. His moves all seem to be based on necessity as he's pretty much the most serious guy on the court.
If Tanishi tried to use Big Bang on Duke I'm sure it'd just have no effect because Duke is so far the physically strongest guy in the series, just like Kawamura's Hado ball normally blows other people's racket away but has no effect on Gin, who starts out with higher strength than Kawamura. Racket busting effects, the way I see it, is a comparison of the user's strength + tech strength versus defender's strength + tech strength.
There's two things here: tech strength and user strength. Muga can copy tech strength. For example we can say Black Jack Knife is unconditionally a better move than Jack Knife, so copying Black Jack Knife gets you better speed/power/whatever than just copying Jack Knife. That's perfectly fine.
But copying Black Jack Knife doesn't get you Oni's strength. Just like Oni's BJK must be more powerful than Momoshiro's BJK, if Ryoma copied BJK it'd be even weaker than Momoshiro's BJK because his base strength is lower. Otherwise, you should just go to talk to Duke and ask him to do some moves, and boom, you get Duke's strength! Copying Duke Homerun would instantly make you top 5 amongst all characters NPOT if you can copy the user's power.
Muga normally copies all-or-nothing moves. For example the ZSS does exactly one thing. There's no 'stronger' or 'weaker' version of ZSS. If you can do ZSS the ball just stops rolling when it hits the ground. Even if Nanjirou did ZSS, it's not going to have any more effect than merely dropping and stopping because there's nothing to add to the tech.
Right now we have a rather unique problem in that there are NO tech moves that can overcome a 10-baller tier character. While Ryoga and Shuuji almost certainly possess such moves, they've yet to show anything so there's nothing to be copied. The only moves that might even have an effect on a 10-baller tier at the moment would be:
1. Zero serve (might be copyable, but its side effect is well-known).
2. Phantom (doubtful it'll work, but Phantom is an extension of Tezuka Zone which specifically cannot be copied)
3. Atobe Kingdom (this appears to only be possible due to Atobe's superhuman eyesight. World of Ice has not been copied either)
So copying tech moves is useless until Shuuji and Ryoga shows their moves (they strike me as the tech-type player), and I assume you cannot copy the user's power. That'd leave Ryoma with no useful moves against Oni.