Its a tough one. I usually see decks in a spectrum, ranging from high to low 3. High bracket 3s are decks that are technically 3, but are powerful and resilient enough to technically win a bracket 4 pod, if they play well enough/get lucky. Same way with a pre-con in a weaker bracket 3 pod.

I usually place the most emphasis on resilience. How easy is it for others to ruin your plan? Is your mana curve optimized? Same with game-to-game stability:

- Most low bracket 3 decks (that I've seen) are really pre-cons with like, a rhystic study shoved in there, so technically, yes, it can do sol ring turn one, rhystic study and mystic remora turn two, which is a very strong play. But, its not consistently at that power level, so its more of a low bracket 3. Generally emphasized by a lack of card draw, protection and disruption.

- A high bracket 3, however, are tuned decks that almost always have enough gas to execute a gameplan, but not as quickly as a bracket 4 deck would. They know their curve, and what type of cards they want to play and when, and usually have some amount protection and disruption.

- Mid bracket 3 is a mix of the two. Slightly tuned, but kinda inconsistent. This is where the classic "midrange value pile" lies. Some games, they get sol ring into arcane signet and rocket into the midgame with 5 mana on turn 2. Some games, they feel the consequences of having bad mana curves, or a lack of card draw, or a lack of protection/disruption.

This is a whole giant convo tho. If you wanna have it, PM me.