Well, I did up a really quick and simple one here. It only accounts for the variables you mentioned -- Defense, To-Hit Debuffs, and Resistance -- and tells you what percent of damage over time you can expect to hit you. It's very basic; it doesn't account for Regen and it doesn't tell you specifically how much DPS you can expect to take, but it does allow you to see in an abstract sense how Defense and Resistance interact.
It's not a difficult calculation, though. Subtract defense and to-hit debuffs from base to-hit (50% for even-level enemies), then multiply that by 1 minus your resistance. For example, start with 50% to-hit, subtract 10% defense and 5% debuffs, and you know you're going to take 35% of incoming damage. If you have 25% resistance, then switching percents to decimals means you take (1 - .25 =) .75 of what damage does come in. 35 * .75 = 26.25, so you can expect to actually get hurt for 26.25% of incoming damage.
De minimis non curat Lex Luthor.
I have exactly what you're looking for; it's right here.
Where to now?
Check out all my guides and fiction pieces on my blog.
The MFing Warshade | The Last Rule of Tanking | The Got Dam Mastermind
Everything Dark Armor | The Softcap
don'T attempt to read tHis mEssaGe, And believe Me, it is not a codE.
Does anyone have or know of a program or spreadsheet to compare mixtures of Defense and Resistance as it relates to average damage taken over time? There are variables with level, critter type, damage type, etc., but something would help.
I have a EM/DA Brute that I made a bit ago and was thinking about respeccing him and making him an incarnate. He has a mix of Defense/ToHitDebuff and Resistance. I would like to determine a "sweet spot" since he can't soft cap Defense and max his Resistance. I figure there are ranges of Def/Res that might offer the mathematical average for best survivability over time. I can get more than one alpha, but I think he will benefit the most from a Cardiac Rare, but finding out if I should allocate more to Def/Res would be helpful.