I realize this might be a difficult topic to discuss within the rules of the OF but I'm going to do my best to color within the lines. If I'm not saying exact websites it's because of that.
As a raid community we like numbers, particularly big numbers. I understand that the dev team is looking at reducing the job synergies in order to open up alternate party compositions and I'm hugely thankful for that... but then there's DNC.
I'll preface the fact that I plan to level DNC first and raid on it in ShB, this is not meant to be a DNC hate thread in any way; aesthetically and thematically it's exactly what I want in a job based on what we've seen so far. That aside I don't see many potential realities in which DNC isn't mandatory for raid content.
The issue all comes back to numbers. People do pad runs now with single target balances, sunoptimal drg tethering and all kinds of catering to a single party member in order to chase their dream parse. You can look at records of any fight and see this sort of sacrifice to group damage in order to boost one member into the sky but it's always very identifiable because very few buffs (really just cards and Dragon Sight) can be focused to one player.
DNC is in a position to change this in a way - it's dps utility is inherently focused on its partner. This means there isn't a choice between boosting the group or a single person the way we can with current AST cards so it's harder to call someone out for a pad run - any run with a DNC in it is in a way a pad run for their partner to an extent.
Saber Dance alone is quite impressive and aligns well with the 60sec nature of many raid buffs. Combine this with changes to AST cards that seem to favor (or even necessitate) their use on single players and it seems like the perfect storm of focused dps buffs that can really skew the average dps of a given job. "Sure, that SAM held 10k but he had a DNC"...
The only way I can really see DNC not being a guaranteed meta spot is if it's personal dps is so low that it reduces clear times to a place that lowers group dps to account for it's buffs to a single player - basically only strong groups can afford to bring a DNC because it's dps contribution needs to be carried by the rest of the group. I don't think SE will do this but it's potencies on abilities we've seen thus far and the fact that it loses several GCDs to it's steps (which have a 1sec recast time instead of the .5 sec recast on mudras) makes me scared for its personal dps.
I understand that nothing is set in stone and that we'll get more info on the 29th. I also understand even the info on the 29th is subject to change before ShB goes live. I'm looking at this from the vantage point of someone who has felt very strongly that the meta needs to be shaken up because an unchanging group composition for most of an expansion leaves things feeling quite stale. I just hope we aren't trading the shackles of BRD and the crit meta for DNC and a focus on selfish dps having a DNC personal assistant.