First off, you should revert the changes because they are unwarranted. A blind blanket reduction only removed nearly all viability for an entire legend, that's terrible. You cannot compare this nerf to the last power blanket nerf because it doesn't relate to it in the first place, we're talking about conditions here.
Now, from there. In the past, Mallyx as a whole was fine until the traits were changed. Sustain wise it was reasonable and had to be timed so that the legend wouldn't be a sitting duck constantly, now the options are all bad like before transfers became a thing.
It's a trait that didn't exist before and should honestly never had, if it had to exist. It wouldn't have had to give Resistance on legend swap, that would had been fine. It would basically contribute as a better Spirit Boon for options that can't really contest it, Diabolic Inferno is mediocre, the Transfer is too weak at 2 conditions and being telegraphed. See more though, because I like the idea behind but it can't exist with everything.
Something that had remained the same for years, changing it's Resistance duration basically means nothing now, 2 seconds was just enough to do anything in compensation, 1 seconds allows NOTHING to be done. It shouldn't be touched at all. This trait is innocent and should have remained the way it was.
It's a mixed bag of problems, there could be better as there is more to it than people seem to realize which I'll explain below. Regardless, you can't have FT or DD, in my personal opinion it doesn't matter which gets to be removed because while DD is slightly stronger, it had been like it was for years too and nobody complained. As long as SB and one other trait that grants Resistance is restored, it's all that matters. DD would allow periodical Resistance which is part of the problem while FT would spread Resistance across in a timely matter every now and then rather than every 5 seconds which is a much more healthy /predictable/ endeavor so you can see where factually it can make sense, preferably for Balance, FT should stay at the old 2 seconds while DD should be reworked.
The biggest problem in the room for the legend;
I can hear the people saying that "Oh but we have skills that don't clear conditions at all, why should we care if Revenant has it's own?" because this skill reward players for using it at a peak of pressure and that peak of pressure is only possible with Resistance, prior to ignore that poison exists, it's nearly impossible to make it worth while without Resistance or loss all the bonus health right away.
It would actually be preferable to see DD being reworked altogether, be gone from the game and leave SB and FT to their own predictable patterns that people CAN counter and have EM with it's own set of 2 seconds of Resistance so that Mallyx players don't have to always rely on having to use PA which is a costly skill, runes or traits such as DD, FT and SB. This would take care of a large influx of Resistance and leave Mallyx as the balanced legend that it was before those traits appeared because before DD while still overboard, wasn't able to compensate as much as it currently did with the existence of FT.
If from the start Mallyx had been properly designed with it's Resistance on EM, this whole entire blanket nerf would have been more or less impactful because DD the way it's designed right now with EM allows to bypass the ICD and earn more precious Resistance because of it. For example, if I use PA, that's 4 seconds, then I can use EM right away which is apart to earn another 2 seconds while this goes on the 6 seconds will pass for another PA which will earn me another 4 seconds on top that of which waiting long enough, I can time another 4 seconds in because of the ICD, that's with the trait alone, of course no damage has been achieved unless people have so on decided to spam me while I am on the defensive, just transfer.
Regardless, DD is designed in a very exploitable way that should just be reworked or removed for something else. Have EM given it's own Resistance and let the rest be defined if people care for SB or FT, by removing DD you remove a potential of 4 seconds by itself, removing what made it possible to fill gaps.
Willing to help with anything Revenant related.