You had a poll open for 7 days and advertised it no where to my knowledge. 75% of the people who come to the forum regularly enough to participate in that are the kind of people who would gladly vote in a rule that does nothing other than annoy me, of course you got it passed. I explained how, based on your logic, the only time we could ever need this rule would be if the vote for reduced mastery time made it so we continued to allow old hosts full mastery with no time spent.
"It's not all about you Athos, and it's not just about "hosting" multiple biju. It's about changing which biju people host in the middle of a battle setup or even a biju match and there being no official record (no, the bio does not count) of which is the proper setup. "
That is your logic behind this rule. Since the mastery was changed and no longer lets old hosts automatically claim mastery the only thing you are preventing is people switching to a bijuu they don't have mastered (since in this hypothetical situation people are switching what bijuu they host just before or even during a fight, meaning they'd have no evidence to claim any level of mastery) and claiming D-Rank jutsu of whatever that bijuu provides, when Gedo, 0, 2, 3, 7, and 8 all have basically useless (or literally no) passive abilities, especially at the rank that you can explicitly do next to nothing with them. No one is going to flip a table over that. I didn't read all the topics you linked and I don't have perfect memory but I am willing to bet that none of the topics you linked involve the challenger trying to strip the host for handicapping themselves and make the challenger have an easier time. I am willing to bet that has happened 0 times.
So if you feel the need to ask the council to warn me for not following this rule good enough go ahead, if they tell me to change my pages further I will, I'll just die a little more inside. Every time we have a council election I will be making a 7 day poll petitioning for this rule to be revoked on grounds of it being obsolete upon its creation. I'm sure after a while people will agree just to make me shut up.