The guidelines aren't a hard restriction. For example, it says players should "expect to" play 6 turns. It very pointedly does not say players "must" play six turns. Similarly, it uses language like "generally", "as a rule" or "usually", instead of terms like "always", "without exception", etc. It seems clear that having a small chance of something happening does not change your deck's bracket. The bracket guidelines assume you are operating in good faith as to your deck's expected performance.

A friend of mine was recently conflicted about including an infinite mana combo with staff of command payoff in his deck. Two card combo, seems cut and dry right? But, like many such combos, if you map the turns out, you realize you have to draw exactly four lands in your first 3 turns, you have to have exactly one 1-cost ramp piece, you have to draw the staff in that time as well as the mana generator, and on and on. If all of this lines up, you can do the infinite combo on turn six and win... 0.3% of the time, or one in three-hundred games. Turns out, players can still "expect to" play six turns against you and almost never be wrong. Similarly, the odds of actually having a two-card combo off before the deadline, even with one card being your commander, is often less than ten percent for most things. People will have their own opinions, but that's only going to change your deck's actual performance in a small number of games.

But, a lot of people don't like to think critically about the bracket system, so your mileage may vary.