Spare me the insulting tone, we can have a productive discussion without it. I have done math on it some time ago and didn't recall there being sweeping losses. Much of the clamor of which there is plenty, is from people who do not do the math as you do, they simply hear other people say, "we'll lose some threat" and broadcast it to the world, "ZOMG WE'RE ALL GONNA DIE HORRIBLY!!"
Thank you for the simulation, that is helpful. I'm unsure of a couple of elements of your simulation: Did you handle main-hand only using RS procs for dual wielding? (don't think we ever established if that was the case or if off-hands could apply it as well) As for % of your threat coming from RS that seems terribly high, my personal tanking with Frost has put it in the area of 15-30% of my total threat at most.
In the end, the real issue at hand is how the loss in RS balances out against the gains in many other things and the lack of change in a couple items. This is always the consideration in dual wielding, though now the balance is shifting.
RS will slide a bit, white swings and -strikes will jump up a bit, and non-weapon based attacks will remain the same. So here's where simulations don't help. Players will use their own methods and sequences with spells, as mitigated by latency, attention, and other human factors, and practical %'s will vary.
I'll steal some values from a previous set of calculations I did on the buffs to strike values (about 20% gain in FS, BS, OB, PS dmg rounding down to be conservative), along with a recent log for 2h frost tanking I did, and borrow your values for RS (25% loss in damage, 10% increase in RS's used, awful butchery of your values in reduction, forgive me). Here's how the breakdowns compare:
*disclaimor, this is probably pretty horrible for an actual breakdown, but the proportions shouldn't be horribly skewed for the sake of illustrating the trade-offs*
2h Live % breakdown on threat overall (Ulduar25, generalized for ease):
22% Howling Blast
19% Frost Strike
17% Rune Strike
9% Frost Fever
4% Blood Strike
3% Blood Boil
So, if we lose 25% damage per RS, but get 10% more of them, that's a 17.5% loss in RS threat. HB, FF, and BB will remain the same, all being spell damage and not weapon-based. FS, OB, and BB will get a 20% damage/threat buff from ToT, and white swings should increase by roughly the same proportion.
The new breakdown would be:
21% Frost Strike
21% Howling Blast
13% Rune Strike
8% Frost Fever
4% Blood Strike
3% Blood Boil
With a net gain of roughly 6.8% threat overall.
The loss is there, yes, but the severity isn't so grand. If your RS is in fact 50% of your total threat, then you will be losing almost 9% of your total threat from loss of RS threat. If that other 50% is a breakdown of say 15% HB, 30% OB+FS+swings+BS, and 5% FF, BB, etc, then you'd also be gaining 6% from your other strikes and you'd be netting a loss.
Out of curiosity, let's find the amount you'd have to lose on RS to cancel out the gains from ToT on strikes, taking 18% loss of RS threat and 20% gain of strike threat:
So drawing from all of our many assumptions, your simulations, and my relative breakdown on potential damage proportions, the break-even point would be with Rune Strike around 40% of your total damage.
RS % of total threat FS+OB+melee+BS % of total threat Net Change
50% 30% -3%
45% 33% -1.5%
40% 36% 0%
35% 39% +1.5%
30% 42% +3%
25% 45% +4.5%
20% 48% +6%
15% 51% +7.5%
Personally, I've only managed to get that high packing hardcore avoidance gear on Patchwerk Hateful tanking, but I can't anticipate how other DK's play. Purely in my thinking, instinctual, not observation-based, if you are getting that much threat from Rune Strike you are not doing what you could be with all of your active move rotations/priorities/sequences.
And in general, losing RS threat will not lose you threat overall, it will simply bring you even with a 2h Frostie, or slightly ahead mitigating your gains from ToT (as if designed that way >.> hmm).