You got it right,
Paladin is great for main healing, bad for dps, and can be off tank also. Usually use hard armor, shield and mace.
Mystics till today (we'll have to wait to see the class changes in the rebuild server) is ok as support healer and ok for dps, plus the buffs he has. Only with good timing and a train party that knows mechanics could work as main healer. Mystics use staff and robes usually.

In pvp I know mystics were good, don't know about paladin.

Notch and midia have a video in youtube with mystics skills:

and here is another with the healing skills:

I didn't find a good video of paladin skills. You could watch gameplays as this one:

Both classes come with pluses and minuses, and your choice should be made by which minuses you'll be willing to live with.

Paladin, indeed, has very low dps, but they are VERY strong healers and will be always preferred as main healers over mystics. Also, they are very survivable themselves. All new/harder content will always require a paladin to keep people up and mystic will be taken as an extra for the buffs/support.

Mystic, however, has defenitely more dps, feels more mage-y and therefor is also much squishier (dies faster). They can work as main healers, but ONLY if the group plays well. Here you have to think who are the people you play with? Do you have a static? Will you pug a lot? If the latter (pugging), you most likely wont be able to keep them up.

To conclude, it all depends what pluses weigh over which minuses for you But keep in mind that, paladins are main healers while mystics are supports only (in normal circumstances).

Depend how end game dungeon are design (and how mystic will rebuild)

Did we need "2 healers" or not
Paladin are main healer but when all the group take dmg, mystic are a must have with paladin (mystic hot party and paladin focus on single heal the tank or member with boss aggro)

Nigratirus (ID 43) seems to need a lot of AE dmg for trash mobs ... i'm not sur that a mystic can be in a optimize party, except if his "spiral dmg skill" will be enough AE dmg for compensate a real dps class

Usually, ranged dps class are easier in pve encounters ... a mystic can provide 2 strong hot of every party members, rez, some buffs (like speed attack buff, or immu 5sec) and continuous dps with dot and during hot tics

So the question is "is a party can be more easy with a mystic, but not too slowy"
If it's too slowy, players will want to make party with more dps classes
Compare to Aion, parties with cleric+chanter+tank+2dps are often faster than parties without chanter for 1 more dps class

But if I remember well, level 50 dungeons don't have "AE" trash mobs as often as Nigratirus ... the difficulty on lvl 50 dungeon are on the boss encounter, where mystic are generally usefull in addition to paladin

Yep, now we'll have to see in december what changes the developers made in mystic class, i love the class but maybe parties won't really appreciate it.
Also rangers weren't appreciate cause of they low dps over other dps classes. Hope they improve ranger dps a little at least. But mystic, rangers and assasins were good classes for pvp maybe that's why they didn't make them too good for pve, to keep balance...

Yep, I'm not saying is bad or good. One way is to try to have all classes be good for both pve and pvp and I personally prefer that and I think that is a better way to try different classes because if you are more a pve player you can try all the classes and the same goes for pvp players. But is kinda hard to keep that balance and rare to see it in a mmorpg.
Other way is to have some classes better for one thing and others for another. In my opinion bless (and most mmorpg) have this second way and probably thats why mystics are not as good healers as paladins and mages have more dps that rangers, etc.