If you're really all that pragmatic, then I'm really having a hard time seeing what the point is of your continuing to hold out.
At this point, there are basically 2 possibilities:
1) D'Hara makes peace, Luria destroys LV, we go kill Aurvandil
2) Luria destroys LV, D'Hara makes peace so we can go kill Aurvandil
So why do you insist upon delaying the inevitable?
Because LN has yet to convince us that LV dying is inevitable.
You say LV's military is pathetic... we tend to view yours the same way. We got struck in our time of greatest weakness, and we still held out. Our egos are pretty inflated right now (perhaps a bit too much so). Still, D'Hara is D'Hara. If you can prove LV is a liability, or utterly destroy them, D'Hara will drop the matter.
One way or another, we want Aurvandil taken out, but we are also thinking of the post-Aurvandil context. Either LV holds out, and we keep an ally against the realm who has been plotting against us for over four years. Or LV falls, and odds are at least a few of these lurians come to join us and or Fissoa. In any case, D'Hara wins. If D'Hara bails out on LV, our reputation will suffer, and odds are LV nobles will feel betrayed and will therefore be much more likely to re-assimilate into LN.
Because we do believe it's just a matter of time before LN backstabs us again. 'cause sure, D'Hara might have talked a bit about attacking LN... but seriously, the Lurias have been talking about doing the same for over four years. It really didn't take much for the Lurias to break their word. Nobody trusts them, and so LN's word is only so good as our capacity to make sure they respect it.