8 missions 4 of which you get at captain rank are not a pve game made... or something like that. You can still grind the star clusters if you want to level via PvE and throw in the new missions when you hit the right level.
The 8-13 Missions (8 Klingon, 5 faction-agnostic IIRC) cannot cover the levels from Lt5 to LG1. They will provide some variety, but you will still be doing a lot of exploration or PvP missions to level your Klingon. The weekly episodes starting sometime in August will help, too.
Can certainly say that about the new missions, give them a couple of weeks to get all the bugs out of them and they will be some of the best content in the whole game. We can only hope the weekly episodes are of equal quality.
Exactly My klingon characters were made to pvp, I ignore pvp on my fed characters for that reason. unfortunatly I think all but my raptor have done more leveling via the clusters than through pvping, the ques take forever to pop sometimes... now they take even longer.