Then we go into some fallacies like a deck can be 50% of a metagame and be 0% of a top 8. When has this ever happened?
It's not a "fallacy" (you are misusing that term).
It's called a "counterfactual" to illustrate the point that metagame presence isn't what motivates B&R list policy - but performance.
Percentage of the metagame is a serious issue and in general has been the determining factor for most bans/restrictions throughout history.
That's absolutely not true. You are literally just making things up.
For most Vintage tournaments in history, we never had complete metagame breakdowns.
How could metagame presence be used to determine most bans restrictions in history when that data wasn't available???? That's a serious question.
TOs didn't report the metagame breakdowns. Not even for most Vintage Championships. Jaco was kind enough to type up the top 100 or so decklists from the last one, but we don't even have a complete metagame breakdown for almost any other one (Ben Bleiweiss typed up the breakdown for the first one, in 2003).
We only have metagame breakdowns for the MTGO events because Matt and Ryan went in and collected it (and I did so for the first one last year)
Go read the old Vintage metagame breakdowns. E.g: http://www.starcitygames.com/magic/vintage/8912_The_December_and_January_Vintage_Metagame_Report.html
All we had was Top 8 appearances for 99% of tournaments. That's what sites like morphling.de collected.
It is Top 8 appearances, not metagame presence, that has been used "throughout history" to justify restrictions.
Through most of Vintage history, we've used a short hand for % of Top 8s as "% of the metagame," but we were actually talking about the Top performing deck metagame, not the actual complete metagame in the tournament hall.
Since Matt and Ryan have collected the total metagame results, and done something we've never had before, calculating matchup win %.
It would be absurd to restrict a deck that is the 5th best performing archetype, and has 4-5 statistically weak or bad matchups.