If we are talking classes, I see them divided in two groups.

Duskblade and Beguiler are classes that work in literally every team, if you are not sure who else would be in your party you can probably take them and work well with the rest of the party. Everyone likes those.

And then you have Knight and Dragon Shaman... are they bad classes? yes, most of the time. But then you find yourself on a party where you are the only melee character and are in charge of keeping enemies away from your allies... while not having to worry about someone else being the target of the melee enemies allowing you to trap them around you with no targets to hit except you? oh boy... it's the knight extremely good at that.

Dragon Shaman has it a bit harder, even if we ignore the fact that no, you cannot take their vigor aura with a feat, and give them that niche of at-will healing, they are still missing a lot of stuff, basically they are a mixture of low power abilities that you would usually find in other classes that specialize in them and as such they are much better at them... healing, area damage, buffs, party face, durability, etc. you need cha for healing, con for the breath, and whatever you are going to use for fighting, and even intelligence for skill points if you want to properly do party face roles. You are going to be very hard press to find a place for them... but we played a campaign that mostly happened in the phlogiston (Spelljammer adventure), and that meant that divine casters could not really recover spell slots, suddenly the healing abilities of the dragon shaman looked much more favorable, add the good amount of NPCs that were with us in the ship and those auras were more and more appealing... basically it is hard, but you can find yourself in games where dragon shaman becomes a really good option.