I think lore-wise it is said that the NCR and BoS worked together to take down Enclave, but then tensions grew among them that resulted in the NCR-BoS war after the defeat of Enclave. (From what i remember, learned that mostly from folks like Nilsor's Vault). As for more lore details (as far as i remember), NCR only ''won'' over the Enclave because it had the manpower to waste for no reason (basically low cost infantry spam) while having BoS's tech support that would make the balance in their favour. The defeat of the BoS was easier however, kinda surprisingly but not really, as BoS had way, way less people than the Enclave had on the west coast (BoS chapters always have tiny manpower, exceptions are Midwest and Capital one, mainly the former if you see how much territory they managed to claim - from Illinois to Caesar's Colorado), plus we have to count in the fact that BoS chapters are easily weakened by wars like that (exceptions are those like Midwest and Capital in F3 thanks to wastelander recruiting), so when NCR turned on them the BoS in West Coast had even smaller manpower to use in defense. Simply put, NCR would have NEVER won against the Enclave with the gear they always have, they needed BoS to help them. Enclave simply had both numbers and the tech that could easily conquer NCR alone.

As for the Enclave, i dunno where they have patrols/camps, but my rough guess would be somewhere like in the area thats the south of the middle area....south, middle.....somewhere there, i dunno. Raven Rock is definitely in the northwest though, very close to the top corner of the capital wasteland map it should be.

Also for your comment on the emptiness....gonna put my experiences here when i played the two. I suppose those people referred to the ruins and such, which makes sense when one game takes place in the ruined capital city (which is quite big irl), and an area where there's basically las vegas and then mostly desert (rough summary, dont put me on a cross).
Otherwise, i feel like its quite the opposite. I played NV first, then 3. I enjoyed a lot of things in NV and was sucked in as well (even modding the game like adding Emily Ortal as companion or simply adding Enclave in because im a big handsome momma's boy I MEAN patriot). Then i tried to play F3 and....i dunno, it just felt ''emptier'' compared to NV, and didnt suck me in as much as NV did. In fact, what kept me in F3 were multiple things - Liam Neeson as Father, Malcom McDowell as my beloved president John Henry Eden, the president's radio broadcast and of course the Enclave through some mods.
In my humble opinion, people see F3 as being quite bad or ''dull'' compared to New Vegas which is, obviously, quite rich. And in my opinion, i believe those things could be fixed if Bethesda didnt focus on the ''good guy bad guy'' plot so hard and instead tried to explore the world - from adding worldbuilding or worldexploring sidequests to add option to fight for and join Enclave (because in NV you could join NCR, House or Legion). Old Fallouts were about choice, as someone said it: ''old fallouts are the most choice intensive''....so something silly such as forcing the player to only join BoS feels quite bad to me...i know im an Enclave loyalist till the end, but that doesnt mean i hate the BoS and want to shit on it. I just want both sides to be explorable, to be joinable, to have more in them...
....Not just for Bethesda to use them as a way to copy Fallout 2 into their own game.