THF vs DNC in same party with same buffs / debuffs, THF will do more damage. Problem, again, is that you're limited to 6 slots. Why bring THF when you can bring WAR (Warcry for other DDs in PT), DRG (Angon), DNC (haste samba, steps), etc. The straight damage you lose from DNC instead of THF, you more than gain from having haste samba and / or steps...
I hope beyond hope, that they revisit job balancing. They acknowledged it was up there on the survey in their follow-up to it, so maybe I'll get my wish on the 30th anniversary.
It never used to be this way, because I distinctly remember THF at one point being very close to 2-hander damage in terms of DPS. THF was almost always used before DNC, I would say DNC's current use is more of a modern adaptation of a DD (I still remember CPing in Dho Gates and people laughing "what does that job really do?). People didn't know where to fit it into groups; it couldn't tank well, couldn't heal that great, there were better jobs for zerg (pre Nyame Grand Pas shenanigans, you just brought Mighty Strikes WARs or SAMs to everything), and it was just a niche dagger user that very few people valued/understood. The only time my DNC for years ever got invited to stuff was during the Qiqirn Ambuscade. People like Xolla used it heavy in the JP community, but I don't remember seeing it among NAs until recently.
THF was stronger than DRG before WSD traits. DRK was very slow when LR fell off, and MNK was highly undervalued as a "Weaker" DD (still kinda is, wrongly). Pre Nyame, NIN couldn't keep up with THF at all, and neither could BLU. Everything shifted after Nyame introduction. And Savage Blade of course pretty much destroyed the spike DD landscape, because now everyone could deal damage. So why bring a THF who can ONLY do damage when you can bring a COR, BRD, RDM and DNC who can deal damage AND add buffs/enfeebles? THF didn't age well.
Go back and look at any older videos of harder content clears, there's almost never a video with a DNC in it. There were no "travelling" events like Sortie or Segs where you might want Jig. Box Step and Haste Samba just weren't as mainstream in the rotation of allthebuffs, you normally just brought GEO since Geomancy was absurdly broken. Now that everything nerfs Geomancy, you're forced to bring a secondary source of Defense Down after Dia3 to guarantee attack cap. And of course with the high introduction of PDL gear and Aria, now you really need to hit that cap to see numbers, so DNC fit in perfectly when Geomancy got knocked down a peg. Climactic is also incredibly busted, and THF has nothing comparable to deal that kind of spike damage that quickly. THF simply had nowhere to fit in, just like Veydal said.