TL: DR I was interested in some math to confirm mitigation >> accuracy when considering less than 100% debuff uptime due to f/t resist bosses have had since 2.0. Definitely no benefit to accuracy.

If you want to read I'd love comments on my assumptions, for knowledge stake:

Shadow tank, and like most I build for mitigation and only have default accuracy plus the 3% technique mastery and 1% bonus from companion affection. This was always based on the assumption that mitigation was better than accuracy, without anything quantitative behind that assumption. Looking at your text dipstick you note using the assumption of 100% uptime on accuracy/damage reduction debuffs, but after a string of bad RNG I started wondering about the actual modeling for debuff uptime and the tradeoff between accuracy and mitigation. I started with this (my first theorycrafting venture) but this was pretty convincing so I stopped.

__Debuff assumptions just to confirm my knowledge:__

Shadow: 5% accuracy and 5% damage reduction

Guardian: 5% accuracy (armor debuff irrelevant)

Vanguard: 5% damage reduction (not considering riot gas due to long CD)

I could be wrong on Guardian/Vanguard since I’ve only played them casually.

__Shadow Slow Time Scenario__

For shadow slow time, if you assume activation every 10 seconds and duration of 15 seconds a miss would lead to 5 seconds of downtime per cooldown for every miss. With 6% misses, on average you have 3% downtime and on average 0.15% more damage taken due to debuff downtime (5% more damage 3% of the time). I assume 10% F/T resist on a boss is correct.

Swapping an oriconian for dread forged implant would be a ~1.3% accuracy gain and ~125 mitigation point loss. For an isolated shadow and its slow time debuff, you’d now have ~4.7% miss, ~2.4% downtime, and 0.12% more damage taken on average than with 100% uptime. Using dipstik’s chart a loss of 100 mitigation points (2600 > 2500) would be ~0.35% more damage taken (~0.29% post-2.5).

If I’m not doing something wrong it’s currently a tradeoff of 0.03% less damage by taking one implant with accuracy (and improving debuff uptime) for ~0.44% more damage taken from mitigation loss (125 points at 0.35% per 100 points mitigation).

I hope I’m reading your work correctly and basically yeah, it's way not worth the tradeoff.

__Couple added points:__

1) I’m not considering redundancy, e.g. shadow-shadow or shadow-vanguard arrangements on the same boss. Then one would have to consider a significantly lower cumulative miss chance (0.1-0.2%, but I don't know vanguard accuracy) and even then you’d have to assume rotations are in sync. So this only applies to solo content or split tank scenarios.

2) For the current shadow, the implant change would also affect health pool and self-heals, but I don’t know how much that affects your mitigation calcs.

3) I won’t attempt to model accuracy debuff and its effect on m/r attack mitigation and overall ‘squish’ profile. Of course in the case of Force Breach you could time the attack such that you’d require 2 consecutive misses to lose the debuff, so assuming 100% uptime is probably appropriate.