TANK -- raw dmg-reduction and/or hp gain. basic i-win vs. dmg button. can be slow or long, insta or over time, etc. DMG means you tank dmg somehow or another.
BREAK -- basic i-win vs. cc button. again it can be slow/long, work for some types vs. others, etc. BREAK means you use a cooldown to get out of cc. Can be used offensively or for utility, but mainly talking about a defensive context in terms of responding with healing or peeling.
In the sense that both TANK or BREAK are used in arena, basically most classes have a large TANK/BREAK ratio. This is problematic because:
- It is much, much easier to "eat through" someone's BREAK capacity then their TANK capacity.
- It is much, much easier to control 2/3 people all game then to threaten them with death all game.
- If you swap targets a lot, you have to eat-through twice as many defensives (TANK as well as BREAK on multiple chars).
- Thus, its WAY more efficient to train one person into the dirt with damage the entire game, slowly eat through their (e.g.3-4) TANK abilities, and blow cheap disposable CC on quickly eating through the other 2/3 peoples weaker (e.g. 1-2) BREAK reserves, which are small relative to TANK.
- If you pick one target and force them to burn TANK while the others burn BREAK, you rapidly transition into a middle-game or endgame scenario where there is little in the way of counterplay, dynamic target swapping, or complex multitasking.
- The hardest part of the game (or in some sense the part which contributes the most to winning) is coordinating 2 kinds of cc (e.g. mage with druid).
Because the TANK/BREAK ratio is high, you produce game physics involving solo target training, less swapping, and more of these hold cds until all-in cc-rotation+burst windows become active. This is synchronous play, whereas in e.g. TBC you had a lot of asynchronous play where people would stagger out (instead of stack) their abilities in order to do differential amounts of pressure to different targets at different times -- resulting in a different kind of outplay and win.