If I was under the impression that you had someone on your team that a single targeted ban would wreck, I'd probably do it. If Hedgie could only play Anivia mid, I'd ban her out as long as we didn't need something more important done with bans.
If i only played Anivia, you knew this, invited me to a game, put me on the other team, then banned it, i would leave the game. If you didn't want to play with me - only win against me - then i want no part in that. If you accepted me on your team, then the opponents banned Anivia, and i lost every single game playing as xxxxx then you would pretty quickly stop inviting me, i think.
Now, we were in Go4LoL or some other somewhat competitive environment, then that would be totally different.
Anywho, your way is certainly nicer, but I personally wouldn't be pissed if Bryff's kass was banned out as a targeted ban - I'd probably just cycle him to adc/support if I was concerned.
The problem is two-fold:
(This is purely from a competitive argument viewpoint)
1- Bryff has a shallow champion roster.
In the past 7 months:
Kassidin: 128 games, 59% win
Taric: 47 games, 53% win
Corki: 27 games, 33% win
Everybody knows that Kass destroys typical AP mid champions. Since Bryff has a lot of games as Kass, he is going to know matchups better than most people he is playing against, since Kass is relatively unpopular - not like Viktor levels of unpopular, but still an uncommon pick.
2- Sharp has a shallow mid champion roster, and with the people we typically play with, mid is the best role to cram her into.
Unfortunately, she doesn't really play very many ADs. Since Gotnades plays a lot of AP tops, and Kog does a lot of AP damage, it'd be pretty easy for us to put GP mid against him every game if she actually played GP.
So we make her play AP mids, she gets predictably wrecked, feels bad because Kass gets out of control, then gets trash-talked.
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Banning out Bryff forces him to either play Taric (or we could even pick Taric early-on and deny him that), and also helps mitigate #2. Now, her mid isn't that strong, and she still might lose the lane against other players, but she probably wouldn't lose it quite as bad.
Suddenly, instead of basically giving you a free midlane nearly ever game (okay, he can play a Karthus mid, 11 / 55%, but Orianna stomps Karthus. Ori also beats Ryze).
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However, the real problem with this all, is it devolves these games into a predator-prey dynamic.
Rather than about letting each weaker player play as well as they possibly can, so that they can contribute and do things like get quad-kills, it's about making each weak player play as shitty as we can make them, then having the stronger players feed off of their weakness, and go 15/1/9 against a 50-win support that mostly plays bot games.
Although getting "fed" is how you win the game, it is a zero-sum game. A player who routinely goes extremely negative KDA because you're camping their lane / banning their best champs every game, is just going to go play against randoms.
i don't think anyone here wants to have games where each team has one or two champs that are 10/1/15, going out of control every team fight, while the poor 1/10/5 sacrifice themselves, because we decided to ban out people.
This also completely ruins any sort of "balance" with teampicking. If we are going to do "oh you have the best AD we get the best AP" then we ban out all of that persons one champions, everyone needs to rotate around, and now your comp is screwed... yeah.
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That said, i don't have a problem banning out the best champions of someone who plays multiple champions in a role - Karl, Thunder and Gotnades are the best three examples. Karl has multiple junglers, Thunder can play every support, and Gotnades has an extremely diverse champion roster.
Here, you're "respecting" their skill, and saying "we don't want to deal with Karl's Cho'gath", "we haven't been able to deal with Signed top - we need to ban it", "Nunu + Kog is too strong end game for us to win teamfights against", "we're confident that Hecarim is Krdax's best jungle, but he can play a few other jungles so let's take that away from them since we struggled with it last game".
"LOL let's ban Bryff's Kass (Hedgie's Anivia) every game so they have to play champions and roles they are unfamiliar with so we can win, espiecially since Kass causes a lot of trouble for the champions we want to play".
That's not my assessment of bryff's replacement (though I did explain my wonderful ability to handicap skill in lol).
i'm pretty sure you're smart enough to realize the highest rated plat player on all of our friend's list going onto the team that has been winning all night is going to cause some problems.
Not to mention the "comradeship" problem.