I dont think anyone understands what your talking about.

Offensive is pretty simple. Either you do magical damage and want the cooldown reduction and spell pen or you do physical damage and want the attack speed and armor penetration.

Its pretty straight forward. Hence why you got no reply.

Read the tooltip. or the post right above yours.

Brute Force adds one damage per attack. Alacrity adds 1% attack speed per point.

Neither of them are better than the other 100% of the time because of the relationship between damage and attack speed when it comes to DPS. As a general idea, buffer the stat that is less common in your item builds.

Honestly it makes minimal difference, but I understand that it's one of those small advantages that there's simply no reason not to take advantage of.

In general, the 21-point mastery build is this:

Tier 1: 3 Points in the Critical Strike Mastery, 1 point in Smite/Exhaust mastery if you have the spell, otherwise 1 in the AP one
Tier 2: 4 in Cooldown, 4 in Attack Speed
Tier 3: 1 in Magic Penetration, 3 in Armor Penetration
Tier 4: Nothing (Brute Force Sux)
Tier 5: 3 in Increased Critical Strike Damage, 1 in Improved Rally (if you have it, otherwise go ahead and take a point of Brute Force, since it beats Offensive Mastery)
Tier 6: 1 in Havoc