Serell attempts a reductio ad absurdum, showing how the logic of 'whoever gets top ballot wins' mentality is false.
You attempt to point out a flaw in the reductio ad absurdum by 'either way,' in an appeal to the explicit ballot rules, however, it doesn't apply to what Serell means. We'll examine that a little more later.
Furthermore, Serell doesn't claim the decision to be entirely up to Sakurai, he merely said he makes the final decision.
You've acknowledged there are implicit rules to the ballot as well alongside the explicit rules such as 'video game character only.' Firstly, you say he can't pull a Sakurai (and while I may disagree with this on the basis of precedent such as Wii Fit Trainer and previous ballots / polls, it shows you know there can be implicit rules). Secondly, you acknowledge that Master Chief is as ridiculous as Goku.
In fact, you've entirely gotten Serell's general idea, and agreed with it, without realizing it.
Serell attempts (and doesn't do a good job at) clarifying here the implicit rules he meant: Being far outside of Nintendo, utterly unrelated, too adult, etc. are all unspoken rules.
Therefore, Master Chief's chances are equivalent to Goku's: they are logical impossibilities both, both absurd, both ridiculous, and neither will ever get into the game, no matter what the polls say.
Strangely, his end goal is to illustrate the point that Sakurai abides by implicit rules.
Oddly, your other goal was to illustrate that Sakurai abides by this one explicit rule.
In the end, somewhat unrelated to our misunderstanding, this explicit rules doesn't contradict the implicit ones Serell speaks of.
Nobody is stupid enough to think that Master Chief would be a better substitute to your sentence structurally, or to your meaning in that particular sentence. It's apparent to everyone that would be implicitly contradictory to what you're saying--something like saying that square circles can exist, they deny each other by their nature. Everyone knows what you're saying about Goku, nobody denies it, not even Serell.
Serell means something entirely differently than what you think.
Again, your tautology is correct: Master Chief wouldn't fit into that sentence, but, again, Serell isn't meaning to replace Master Chief in that particular sentence.
Serell means to replace his initial comment on Goku, the first one quoted in this post, with Master Chief, not your criticism of his initial statement.
And this is the crux of the matter. Unwitting to the intention of the other, there was the thought that the other was responding to one's own points rather than the other's own. One was talking at, not with.
This interpretation of events is the most likely accurate one if we are to believe Serell can do the basic logic all humans think by, and that misunderstandings are indeed a common feature of human interaction.