Unlocking aside, my first impression that a TP-based healer would be useless in anything that can put up a fight was 100% accurate. It briefly was acceptable in Abyssea, but only because Abyssea is more about running around killing stuff quickly, and even in Abyssea didn't have any useful procs since new jobs got totally screwed on weapon types and, let's face, it you were bringing a THF.
Most fun job in the game. Totally useless for anything other than screwing around.
I main healed all the time on Dancer back in the day. Everyone would be scared that a dancer couldn't heal a party, but it totally worked. It didn't work so well on endgame mobs, just 'cause everything was impossible to hit without a bard.
Low man? Worked fine as both a tank and a healer. Solo? You bet. I dunno why people only gauge a job by it's ability to perform in the biggest 18-man fights around... I spent maybe 5% of my time doing those, at best, even in a fulltime endgame shell...
It's also weird to me that in a game so heavily skewed towards haste spam, a job which provides yet another party-haste gets seen as useless in big fights... especially considering that, once everyone is good and buffed, that last 10% haste can be gamebreaking to anything but DRK (just 'cause DRK caps JA haste on its own).
Then you have another -13% defense that stacks with every other def. down, and up to -34 evasion (Desperate Flourish + Quickstep 5/5) back when accuracy was actually relevant and 80%~ acc was considered the norm...
Honestly, I think Dancer was, and is, vastly underrated. It suffers from the fact that its contribution is not blatantly obvious. If a bard gives you march and minuet, you see the little icons and think "Aha, that's why I'm strong." If a Dancer gives a party haste and lowers the enemies defense, people just assume they're swinging fast WSing hard because they're good or lucky.
It's the same reason that so many people never realized how much a difference a quick Dia II could make. I feel like Dancer wasn't really meant to fill the healer role at endgame... it was meant to debuff the mob and provide more almighty haste.