Same here. I remember in FO2 I absolutely did not want to piss off the guards in any given city until I had really good equipment, because otherwise I'd get stomped.
Really, anywhere that is supposed to be a major base should be (near-)suicide to assault unless you have the absolute best equipment, since the assumption is that such places would have the best troops guarding them. Now, F:NV gets this right to an extent, since the quality of the guards in McCarran and The Fort improve as your level increases. However, their weaponry does not keep pace nearly as well, since even when they have top-end gear it's in terrible condition and is only putting out, say, 25% or so of the damage it should be dealing.
FO1&2 handled this well; only an idiot would assault the Master's stronghold (FO1) or Navarro (FO2) without the best gear and/or at a low level, since the defenders were heavily armored and armed and would destroy you in short order. In contrast, assaulting The Citadel or Raven Rock in FO3 was ridiculously easy even with mid-tier equipment. Of course, a large part of that was the fact that FO3 PA was an absolute joke...
In NV you could probably fix it with a few quick MODs: reduce the PCs personal DT, increase the rate at which all armor deteriorates in condition from fire, make special ammos far more rare with vendors, so the skill with making them becomes more necessary, and make the best weapons more rare, so some of them aren't even sold by vendors, but found only with certain factions. Increase the time it takes for enemies to stop looking for someone when they see a dead body, reduce the availability of stempacs and make doc bags harder to come by/make, etc. and upgrade the weapons of the soldiers.
... granted, by a few quick MODs I don't mean all that stuff would be easy, and I don't have the game on PC so I don't even know what files are accessable. Other than that... leveling, I never liked it. Going up in level means I should finally have a chance at taking a small group of raiders more easily, not that I have an equal chance at 1st or 30th level because they scale with me. some should just be low level like the crappier raider bands, some should be hard so you can only take them on at higher levels or with really good equipment, and some things like killing everyone at camp forlorn hope or camp golf, should be a challenge for even high level players, and suicide for low level ones-- even with great equipment.