Yes. The idea of a 'selfish DPS' is flawed. It's the most perfect of imperfect solutions, however. What was the alternative? A raidwide crit buff? We have those. Raidwide damage buff? Got em' in every shape and form, don't need more homogenization there either. If you want every new Job to boil down to people wanting them for their own "TA" or "Balance" you want a really boring game. That being said, it's no one here's fault that they're seemingly running out of ideas for 'synergy' and 'utility', so no reason to debate the design of SAM being flawed.
Speaking of utility and synergy, though... It is absolutely the right idea for them to be lower than a Job with less. It's a balancing board. The more of one thing you have, the less of the other you should have, by nature. So, while you aren't entirely wrong about why certain Jobs are more alluring, and there are certainly other moving parts... The real reason people want NIN/RDM is because there's no downside to bringing them, and they have the most of everything, without sacrificing much of anything. Total contribution to the party dwarfs all, and they have the highest without a doubt.
The above being considered, it is actually more of a liability to bring a 'selfish' DPS than any other Job. Alternative means of supporting your party means that even with Weakness, or Brink of Death, even if you mess up mechanics, or have low mastery over your Job, you're bringing a static value that will improve the raid. A selfish DPS has everything to lose. A DPS with synergy/utility has static support values that never diminish.
And finally... SAM is no more easier or difficult to recover from mechanics than any other Job. It just loses damage in ways that people don't understand unless they study the Job. It'd be great if people could stop and just read a little into their mechanics. All people see is Kenki/Sen never deteriorating and assume, "Well, that's just like my Enochian/BoTD/GL, but their's never goes away!" It's not conceptually the same as any of those mechanics, nor is it how the damage is lost on SAM. 5 missed positionals, for example, result in the effective loss of 300 potency. Similar losses occur on the other melee for those mistakes, just in a different way.