Tenacity is just not needed because of encounter design. Boss autos do basically nothing and as long as you execute mechanics correctly, you will have no problem clearing any encounter that you meet the ilevel requirement for. Tanks in particular will simply never be in danger to party mechanics due to the flat 20% DR and large health pool. The only thing that threatens you is a buster, which you have a billion cooldowns for.

Damage on the other hand is critical in savage content. Enrage timers are tight and squeezing out every digit of dps you can is important to clearing.

Until they redesign bosses to threaten tanks outside of tankbusters, tenacity will be the obsolete stat. At most you can stack it if you just want to spam roulettes with huge pulls.