So here's a little experiment to expand on my earlier thoughts. I took the blacksly Fire/Dark build and created an alternative Fire/Rad build that was basically exactly identical in terms of everything except the secondary, which I replaced with Rad. All other slotting in the primary and pools is identical, with one exception: I moved one slot out of the secondary powers and put it in Fire Cages. This is about as close to an apples to apples comparison as you can get. I don't think its optimal, but its a reasonable proof of concept. The build data link is at the end of the post.
Using Mids numbers for damage (so I don't have to calculate those by hand, I get the following damage for Ring of Fire and Char in the Fire/Dark build (assault turned on):
Ring of Fire: 230.1
Char: 136.2
Using my earlier calculation, I estimate the amount of effective damage of a single use of TG as being 94.24 * 0.5 * 0.15 * 20 = 141.36. That makes the RoF-TG-RoF-Char chain deal 737.76 damage in 6.468 damage, or 114 dps.
My Fire/Rad build has AM, and thus slightly higher damage. It deals:
Ring of Fire: 243.6
Char: 149.6
Fire Cages: 61.58.
It also has slightly more recharge. It can execute RoF-Char-RoF-FC in 5.148 seconds dealing 698.38, or 135.66 dps. That's actually more damage than the chain that uses TG. Now suppose we throw Tar Patch and EF into the equation. I will presume -22.5% res continuously on the Rad and based on TP's cycle time (28.69s) in the Fire/Dark build the average res debuff is about -47.05. That would increase the Fire/Rad dps to 166.18 dps and the Fire/Dark (keeping in mind TG's -regen value doesn't increase with -res) to 157.4. Interestingly, Fire/Rad's damage output without TG is higher than the Fire/Dark's damage output with TG, even factoring in resistance debuffs.
If we factor in the 95% tohit ceiling, then those numbers drop to 157.87 dps for the Fire/Rad and 149.53 dps for the Fire/Dark.
Next, the bigger regen debuffs. Rad has LR, Dark as HT. We're going to assume for simplicity sake for these long cycle time powers that they do not interfere with the attack chains above. Dark's HT cycle time is 54.35 seconds and HT's debuff is -500% for 30s. I'm going to approximate that it always gets full value for HT, even though it will sometimes be clipped a bit because of TG's debuff above. The value of that debuff is 94.24 * 5 * .15 * 30 = 2120.4, or 2120.4/54.35 = 39 dps of effective damage. Fire/Rad's LR cycle time is 24.9 seconds. That overlaps, and you can't do better than 100%, so the debuff value is 94.24 * 5 * .15 * 24.9 when its single stacked, and 94.24 * 5.1 when its double stacked, for a total of 2240.56, or 2240.56/30 = 74.69 dps. Factoring in 95% tohit ceiling, that averages to 70.95 dps (Howling Twilight autohits, so doesn't need this adjustment).
The net effective dps at this point is 157.87 + 70.95 = 228.82 dps for the Fire/Rad and 149.53 + 39 = 188.53 dps for the Fire/Dark.
I'm going to take your word for it on the Fluffy, and assume it deals 17 dps and factor out the 30% AV resistance for these calculations, making that 24.3 dps. It should probably be slightly less than that because HT should reduce the maximum impact of Fluffy's -regen, but that effect is probably low. That increases Fire/Rad to 212.83 dps.
That leaves the pets. Both builds have the same imps with the same slotting: +96.89 damage. The Fire/Dark has +28.5% damage in global set bonuses and assault, while the Fire/Rad has 48.5% due to the +20% additional buff in AM. So whatever the Imps base damage output is, the Fire/Dark ends up being (1.9689+0.285) * 1.47 = 3.31x base damage, while the Fire/Rad ends up being (1.9689 + 0.485) * 1.225 = 3.01x base damage.
So the question is, what's bigger: 0.3x base Imp damage, or 16 dps. Or alternatively, is there any chance that base, unslotted, unbuffed, zero resistance Imp damage is 53.3dps or higher? I suspect its lower than that.
And this tries hard to keep the builds identical, but in one respect that puts handcuffs on the Fire/Rad. I replaced TG with Fire Cages in the Fire/Rad attack chain, but that attack is horrible. There is an opportunity to juggle the build around and add a better attack such as one from the epic pools. Almost anything would increase Fire/Rad dps substantially. But even with that low DPA power, Fire/Rad looks competitive, if not outright exceeding Fire/Dark on this basis.
The one problem with this entire analysis is that neither build can actually sustain the attack sequences being described, at least based on the numbers I'm seeing. I had to assume that to the extent one can supplement their endurance in a way to power this level of activity, both could.
I haven't discussed EMP yet. Here's what EMP would do in incremental terms. EMP would floor regen for 15 seconds. That's worth 1413 effective damage, and the posted build has 82.15s cycle time for EMP, which would be 17.2dps if used at maximum frequency. But it would also stop recovery for 15s and burn 15.62 end as well, which (at the recovery rate of the build) be an effective cost of about 4.07 * 15 + 15.62 = 76.67, or 0.93 eps. If you had unlimited endurance, it would be worth it. Otherwise, its very difficult to sustain.
In any case, I think a strong argument can be made here that Fire/Rad would outperform Fire/Dark, if only by a small amount.
http://www.cohplanner.com/mids/download.php?uc=1523&c=702&a=1404&f=HEX&dc=78DA65945B4F135110C7CFB65B9052A40591BBD00242299436E2AB1AAEA2142B18DFB42EB0C0266DB76E97441F7C3051E33D06F54318135FBC40FC1CDE62E2836FC644F1F2AC757AFE53D8B89B6E7EE7CCCCFFCC9C397B9ABA341178367DF5A85082E359AD58CC8C9B79DB32B359DDF2A5B4556349949F6A7ABB763D95A0F89461E99549C4E11F5B5F5989CF6BCB86661B663E3399338A451A8466F26BBAA5E7ED7865E04F9BB4CC4241D797037238AB6B0523BF5A5F992CEB5671CD28D4CAF954D6585DB3DB270BC6527CC2CC1979CD36ADCC82B99ECDA4B4A2AD5B975BA8D028BDD715C14FC927DE7884E85485E71DF33DA87E60CE1093AAA8CA9128A28AB95DAD2AD2B0559D04F7CC32538AD426E730BF4150389FB225A4CDBFC97C09065E309F83C39FBC326F0F75D70BADF07EF4485F39AD4FC17ABE0DD4177CC87C04363C06BBEF31EF833749570DADB7DA46AE868BE0BE2C33075EA3B81AAEBB2609FDFE0473046C893387C1B625AFD4DE226D2D6B6BAFA00F6D8BF07568CC0BE0810CF33C788AC2EBA0F5D6BDC2BA0736791F5B60F835384FB1F5DC9FFA9890B6DB640BB13EC4E719E6F30CF379F7BC051728B691CFB391F53D1586C1DE278A64F42918A13369420F3D4D31F4AAD7C9727F28A619314A7313F67FF08F903943E46B657D6BC51764FEC53A6768DACE7B68E79AFB792FFDFCADF6F39E4E973F37CED5C935479977C9DEC5EB741D41CFA2C7C0C131E638F8A0DC7EAE2B7218F50C26C0A151F02CA18FFBD53701DDD024730A1C9E661E07BF0484189037A02406BEA2E60DCA15E3EF23F61BDFF5C836F317F32798E4DE263BC13BB4549CCF3CFE19F7A4817A9A40ED2211465C87BA7357E9474F39315FC55269D0E54DB82C4997E590CB32EAB2CCBA2C6975E71F4028D25213DCB9D7A56F7EF22A4EEFB6D372029DFFEE8AFAB16BF128DDD8F3DEFF98F6CB2A649E738EB1E6182F3AC6FF006FC5FDF0