I ahve played all ending now and some things seem a bit odd.
It's like they all miss something/s.

NCR
All sensible apart from they don't even try to use the securitrons. Surely they would try, at least. Total waste not to try. Having a vast army or well trained troops is a good and sustainable way to fight. but surely powerful robots would help?
Maybe it's seeing it from the outside and they don't know that much about the securitrons to use them. But it is odd, however you think about it.

House
He accounts for every faction but the Great Khans. Maybe they don't figure to him anymore once he throws them off the strip. Or he can crush all and any enemies, so even if they sided with Caesers Legion, they would still not matter. It just does'nt seem a good idea to ignore them completely.

Independant.
It is odd you can't ally with the Brotherhood Of Steel. You can with the NCR. House they all die, which makes sense. You should be able to ally with them and have them help you.

Caesers Legion (bleugh)
They are a big vile, disgusting logichole by default.
But some things really does'nt make sense.
Why the hell would ANYONE try to recruit the White Glove Society?! They're no good for fighting! They are a bunch of fashionistas and socialites! The most damage they can do is by hitting enemies one on one with their dress canes! They don't even use guns!
They're useless in any other situtation! They are only dealt with to get them out of the way for House and a independant. Not recruited.
They're matriarcal and sixually equal, cultured, well educated and very refined, what freaking interest would they EVER have with siding with CL?! ANY OF THEM! They're the exact opposite to CL!
I know that CL are complete and utter morons, but come on!
And the Omertas for that matter. They are gangsters who deal in drugs, alchohol, prosttutes and every vice possible. There is no logical reason why they would side with CL ever. CL is opposite to everything they are! It's not like they ar'nt in the thick of everything and they don't know what they're like!
The GKs I can sort of see why they might be fooled. Given they have been hiding in Red Rock Canyon for 4 years and don't have computers. But it is still deeply unlikely that they would be fooled by CL, surely they have to hear things?!

In regards to the legion, khans are just a means to an end, he's using the papa's hatred of the ncr to his advantage, he cares little/nothing for them, put regis in charge and you see what happens. Omertas, ditto, attack an enemy from within, caesar isn't stupid, he does use subversives (ie; a certain colonel), panic and chaos on the strip, fear is just as good as a weapon as a big gun, White Gloves, i believe when talking to house and/or caesar they explain their dilemma regarding what they are.

With the ncr, i would venture to say maybe they would utilize them, but my leaning would be no, this theory goes in regard to the indie/yesman path, house knew the possibility he would be took out of the picture, hence someone finding programming to make themself a little more agressive in their decision making. (<- please insert correct quote, i'm fairly certain this is wrong, but you get the idea). Think the movie, I, robot, i think the ncr would generally have distrust of any tech house was using after having to put up with them for so many years.

I'll agree that they could have done more with the endings, but for the most part, they are plausible.

I think CL allied with the WGS and Omertas because they want some friends for when they go to the Strip.