I may be misunderstanding, but I'm not sure at any point Suji suggested forsaking buffs from a COR for a THF. As an aside, COR switching a roll on the spot like that--even if you aren't rotating CORs--means you're going to be stuck with Hunter's for at least two minutes (less depending on merits). Not sure that's going to be worth it for the 30 second gain, depending on which rolls are being lost.
As for THF vs DNC, I'm not sure who is actually getting use of the enhanced Haste Samba, unless the DDs have an alternate TP set to account for it.
The THF vs RNG comparison is a little strange unless you're suggesting the RNG is going to be getting the same buffs as other DDs (marches/fighters/etc). If you have a RNG party, obviously bring a RNG. If you don't, I'd bring the THF.
A THF
can be quite comparable to most DDs nowadays, assuming that attack, accuracy and haste are all capped--as this eliminates most of a traditional DD's advantages (MNK's impetus being the first exception to come to mind). If any of those are uncapped, they will start falling very quickly behind.
As mythics become relevant again, the difference in DPS will obviously grow again. If attack and accuracy are once again an issue, it will grow even further. But as it stands, DD jobs happen to be at nearly the same level, thanks to painfully easy content.