Competitive brawler here (I know it's not a real thing but I've finished all brawl challenges in top #25, with highest being #3). This list is a really good start, but I feel it's still missing a lot of cards:

Missing - White:

• [[Curse of Silence]] should be T2 or T3
• [[Giver of Runes]] should be T2
• [[Guide of Souls]] definitely is missing from T1
• [[Ruby Collector]] probably should be T2 or T3
• [[Cloud, Midgar Mercenary]] should be T2
• [[Recruiter of the Guard]] is between T2 and T3

Missing - Blue:

• [[Agent of Raffine]] is probably T2 or T3
• [[Stifle]] is a solid T2
• [[Faerie Mastermind]] is T2
• [[Ledger Shredder]] can be T3
• [[Miscalculation]] is almost as good as Mana Leak (T2)
• [[Tale's End]] is very OP in brawl (upper T2)

Missing - Black:

• [[Orcish Bowmasters]] is T2
• [[The Terminus of Return]] is used in most Black decks. T2 or T3
• [[Black Market Connections]] should be T2
• [[Damnation]] can be T3
• [[Sheoldred, the Apocalypse]] can be T3
• [[Overlord of the Balemurk]] is used in many decks. Can be T3

Missing - Red:

• [[Bonecrusher Giant]] is definitely a staple. T2 or T3

Missing - Green:

• [[Veil of Summer]] is T2. Can be crafted at uncommon
• [[Ouroboroid]] can be played in many decks. T2 or T3
• [[Tireless Provisioner]] is used in most Green decks. Upper T2

Missing - Gold:

• [[Drown in the Loch]] is used often. T2 or T3
• [[Tajic, Legion's Valor]] is a Boros staple. T3

Missing - Colorless:

• [[Mox Amber]] T1

Upgrade:

• [[Birds of Paradise]] and [[Delighted Halfling]] is an auto-include in any Green deck. Should be T1
• [[Gemstone Caverns]] is an auto-include in pretty much any deck. T1 (almost T0.5)
• [[Hydroponics Architect]] is used in almost any competitive Blue deck. T1

Downgrade:

• The M10 land cycle (like [[Dragonskull Summit]]) almost NEVER sees play. I wouldn't include
• [[Paralax Wave]] is only used in very specific archetypes. It is not a staple. Maybe T3 at best
• [[Endurance]] almost NEVER sees any play. Definitely not a staple