"All Jobs can clear content" i've yet to hear anyone who has discredit this claim so the amount of people who sling this phrase around must be doing so to confirm it to themselves. this claim doesn't account for the risk you take when bringing other jobs, BLM lack of utility isn't whats going to hurt you in prog, but it's turret play style will when compared to the more mobile options, SAM's dps isn't so high that MNK and mantra are seen as inferior for progression or the enmity manipulation of NIN and DRG's Disembowel speaks for themself in prog and farm.
I don't think there are many SAM's that cleared ultimate without having done so prior on another job, Also i don't think the lack of utility is so much a problem for SAM and BLM as it is a fixiation of the community on having the best or otherwise better alternatives, RDM sees a lot of hate and it has utility(Embolden is actually pretty solid) because it's personal dps isn't as high and many groups would have a BRD before a MCH if they're not taking both. Groups want the meta even when they don't need it, this game also has some interesting balancing issues since alot of the easier to play jobs tend to be the better to play. MCH and BRD are probably equal in depth but, DRG is much easier than the other 3, and Nin is only slightly harder. SAM has a lot of opportunities to be sub par while MNK is the most difficult to play well of all 4 do to the fact it's rotation is the most susceptible to fight variance. SAM's have more issues besides not having utility
Being unable to contribute meaningful utility means
Death, Downtime persistent phases, High skill ceiling, lack of utility, no defensive options = a job that just doesn't have anything worth looking at thus making it too risky for no tangible reward and i find that to be SAM's true problem. at least BLM has addle/shift which is unique in single caster comps