Is it up to me?

[Naberrie]

So if I combine an archer with an conjurer I will be less likely to be chosen as a partymember for dungeons?

The thing is that any skill you could take from Archer to use on CNJ would be useless in a party. You want to take skills that are useful. Skills like Swiftcast from Thaumaturge, or Eye For An Eye from Arcanist are useful. Raging Strikes and Hawk's Eye are not. Not for a CNJ.

When you solo you can do whatever you want, but when you party remember that everyone else needs you to perform a certain roll. If your damage dealers showed up with Cure from CNJ and didn't do any damage but just spammed Cure, you wouldn't get far. If you show up popping Raging Strikes from Archer and Internal Release from Pugilist, not only will they be no help to you, but your party will probably end up dead.