2005 haste is the Holy Grail of Current Resto Healing. That is not to say Mastery is Bad, it's just not the Holy Grail.
You seem to talk about mastery as if the haste druid doesnt benifit from it - but they do. They have less Mastery, but they still have mastery.
In fact, most people will have a lot of mastery as its considered the next choice after Haste. So we actually agree with you that mastery is good, it's just not good enough to drop the Haste Break.
Having said all this, if you feel you do well with mastery, then continue doing what you want. You are entitiled to do what you want but not entitiled to suggest its the best performance.
If you could make a clone of yourself and compete in a raid, the clone with 2005 Haste would heal for more.