Only s/wd (without 60/70 elites) is any good out of those classes.
Without 60/70 elites, none of the other classes are helpful INSIDE an instance. as others said, m/p can be used as a buff alt outside, and r/m with 70 elite is good dps class, and with 70 elites s/wd gets even better.
if none of these characters are worth a darn then what class combo should I reroll and level?
wl/m (or m/wl) and get the 60/70 elites. These classes are usually in high demand so getting party invites will be most likely if you learn these. These clases also require the least amount of tp, and minimal gold/diamond investment. As long as you have 150-200k hp buffed, so you don't die in vale of rites, your attack power doesn't matter for either class -- resulting in you being able to sht stat armors with m. crit on them (wl/m doesn't "need" anything but hp, m/wl needs crit rate + hp).
(notice. none have elite skills 60/70, need to kill world boss and could also use the help here)
You do not need to be in the party when the bosses are killed. On Mithras, people often world shout "mandara held for elites" -- this i your opportunity to port you characters there and use the beacon of courage on the corpse. If on Erebos, idk world shout a few times asking for ppl to hold corpses?
As to actually getting an invite, as already mentioned, you need to be socia. Most people already have a group/list of 10-20 ppl they know (maybe more if you include guild mates they don't interact with often), who will get priority on invites. In most cases, if a group isn't full from that list, they don't run at all b/c they don't trust random ppl they've never spoken/run with before to not get them slaughtered constantly.
Offering to join ANY run offered, whether its grotto or pillars, or vale, or hall of earth, w/e , will get your name out there, and might even end up running with some of the ppl who do the instances you're really after. Conversations in guild / party can sometimes go
--playerA: we need a wl/m. I don't know any online
--playerB: i ran with person xyz in grotto, they seemed okay. Maybe we can try them in [instance R]
If you keep yourself unkown, you won't get into anything b/c no one knows you exist, and no one will know if you are competant and/or coachable.