During DW, mastery almost equal streangth in value. However hit/haste should still be better then crit when those ratings are so low and you have the 2p 13. The best DPS gain for tendron should be to reforge everything to mastery with hit as second priority.
You would need to take into account the timing of the exposures. If you are killing the amalgamations fast enough you won't have death wish back up for the second exposure. This would greatly reduce the benefit of a high mastery build. You can offset this slightly by popping DW 5-8 seconds early for the first exposure.
In regards to a high mastery build I would be interested to see what would happen if you force procc'd heroic Soulshifter Vortex (3278 mastery). It could obviously require you to stop damage for about 10 seconds before the exposure. The biggest problem I could think of would be if you were getting to the exposures before the ICD was back up.
With a high mastery build I hit 2173 rating (79%) which is a 35% death wish bonus. Proccing the trinket= 5451 mastery (181%) causing death wish to do 56% bonus damage. This would also affect your bonus damage from enrage.
This would cause insane burst for the first exposure, but low damage for the second exposure, and possible rage problems from the low hit rating.