In sum, Damage bonus is nice, because when you're fighting uphill (i.e. against a mob that has a significant AC advantage over your attack rating <i.e. Highest tier raid targets from current expansion>) your damage bonus becomes more meaningful, as demonstrated in the counter-relevant tanking post above.
However, when your dealing with a mob that your Attack rating vs mob ac rating puts you on the higher end of the hit distribution range (i.e. raid bosses nearing obsolescence, or in-era raid bosses which are fully debuffed with ac-debuffs <cripple, nec/enchanter DoT line, Druid AC debuff) you will do better prioritizing base weapon damage over damage bonus.
Likewise, when tanking AC > HP in most cases, except for perhaps AoW, or any other raid mobs that the devs have specifically tuned to have an attack rating so high that current itemization cannot push the mob toward the bottom of its damage interval table (barring the addition of aoe non-physical damage types from AOE/DDs)
Without actually being or extensively parsing the tanking of a top-end raid tank on this server, I cant really advise on how Sirken has tuned the top-end raid content on this server on an Attack vs AC standpoint, nor can i provide specific examples of the ratio of said raid bosses DI
[You must be logged in to view images. Log in or Register.]B ratio.
(AoW was a notoriously high attack rating raid boss in era which is why it took guilds so long to bring him down with tanks frequently being two-rounded and sometimes even 1-rounded while tanking him because of the frequency at which they ate max damage rounds)
I can say that in later expansions on live, the devs do less "mega attack" raid bosses , and instead of bolstering raidboss attack power to unimitigably high values, they just increase the ratio of damage bonus to damage interval so that raid bosses have a reliable minimum damage output capability which sets the bar for healing/tanking reqs with "lucky rounds" being much less frequent.