I'm not quite sure what you mean by "(soft) CDs"?
Do you mean like Circle of Scorn and Sonic Break where the abilities themselves have the CDs and just deal their damage as a DoT instead of a burst for......reasons? Personally, I think that's stupid - messes with the debuff cap and reduce's a Job's capability for on-demand burst damage, which means they're weaker in stuff like Deep Dungeons and pushing phases in Ultimates, the two places that might matter - but I've already said it's more or less the same in terms of execution as just having abilities like Assize that are "use on CD", so I have no inherent problem with it. I would think it's stupid, of course, but it wouldn't really bother me much. They'd need to be AOE in that case, of course (since you only cast the one then it's on CD for the duration, to DoT up multiple targets would require they be AOEs), and it would be kinda weird in a 4 man AOE DoT with the one spell then just running behind the tank casting Regen on them and then planting both thumbs firmly up our butts until the Tank stops running so we can start into the Holy Spam, but...meh, that wouldn't be absolutely terrible. Although...
...I also have to stress: That's more rigid and less flexible than Lily use now. Lilies now recharge every 20 sec, but you have the entire 60 sec window to decide when to use them in (so you don't overcap on Lilies), making this like PLD Holy Spirit. This is a good thing.
Having rigid CDs does not allow this, and is thus not as good a thing.
It'd be better to just to ignore the DoT and do more stuff like Plegma. Like say WHM had an "Aero" spell that generates charges every 20 sec and can stack up to 3 charges, and every time you use all three, you get a "Water" spell that does big damage. This would allow much more flexibility and you could save the Aeros to use all at once, or space them out. Unlike a DoT, you could slam them back to back if you wanted to, and unlike a DoT with a hard CD, you wouldn't be penalized for stacking them or not using them right on CD. Seems better in every way to me, honestly.
Maybe. I feel we already get that with new abilities. We got a more powerful Glare and Holy this expansion, as well as Misery being more powerful, and we got Aquaveil (which is kind of a nice little ability to have) and Lilybell (which my big complaint on is why the hell the CD is so long).
Honestly, I also find the "reinvent the wheel" doesn't always work out so well. Sometimes it works out great (like SMN; and still generates tons of backlash despite working out great), and other times, it works out horribly (like AST). You also have people that love their Job and just want some QOL tweaks getting complete revamps. In fact, most of the time MMOs change Jobs too much, people pine for "the good old days", sometimes for years.
As much as "so people don't get bored" is presented here, it's really not as valid of an argument as people think, I don't believe. And I also think this is another case of "some should get it and some shouldn't". In MMOs, I tend to like the classes that change the least with time, not the ones that change the most. The WoW classes I liked most when I did finally quit were the ones most similar to the way they were back in the Wrath/Cata era. That is, the ones that changed the least over time.
Yeah, one of the big problems with DoTs - no matter the game - has always been the UI. In WoW, almost everyone who used a DoT class had add-ons telling them when the DoTs were about to be up to refresh them. Which defeats the whole purpose, since you aren't "managing" your DoTs, you're just refreshing them with a script/program tells you like a trained monkey. It was kind of unsurprising to me to hear that high end FFXIV players also were using add-ons to tell them this same thing. Refreshing a thing when told to isn't skill, and is actually less skill than even refreshing a hard CD is since at least that you're figuring out on your own.