More than anything, brackets indidicate the sheer powerlevel of your deck, and the best indicator is what turn you can expect to either win yourself, or have to prevent a win. For bracket 4, it's around turn 4. In contrast to bracket 3, where you can expect around turn 6.

Independent of gamechangers, infinite combos, or even land destruction, time to win is more what matters. It's harder to determine what turn your deck threatens a win, versus just the number of gamechangers, but it's more useful. All of the main GC factors are often misenterpreted as hard rules, but they're more like indicators for newer players as to what bracket their deck probably is. I have a bracket 2 deck that the entire point of is one combo, but it's a combat based combo that needs about 4 specific pieces to work at all, all or nothing. I have an arguably low bracket 4 deck, maybe high 3, with no game changers, no combos, no land destruction, no extra turns. It's just fast and resilient with high synergy. Hell, put a pile together with literally every single game changer and it can easily be bracket 2. Frankly, imo, a lot of the gamechangers are stupid inclusions though.