gangers? why gangers? there are Factions with as hi-tech as NCR's stuff.
It is not just about equipment but training, discipline, logistics, etc. Nation building has NEVER been purely military. If NCR "takeover", is possible, then it should be a quest of EPIC magnitude and require many steps.
1. Extensive questing could be done in the way of diplomatic and logistical preperations. Scouting targets, forging alliances, (both through various player gangs and NPC factions) maybe a little assasination quests like the ones in the original games.
2. Once the questing requirement has been completed, we can move onto the combat/logistical aspect of it. Factions would be required to co-ordinate their offensive realistically. IE: Red Dots initiate a massive assault on NCR. If they have an ally (CS for an example), their job would be to secure the 8 squares surrounding NCR to prevent re-enforcement. The assault could be made easier if a "fifth column", has been planted inside the city. Their primary job would be to de-activate defenses and alarms, disrupt command and control centers, and otherwise also assist with the dispatching of NCR loyalists whether they be militia or regular army.
On the flipside, it could be the same for the "good", factions IE: Lawyers. They do the complete opposite by assisting NCR forces and making sure everything runs smoothly. VSB could assist by disrupting CS attempts to block re-enforcements.
Its just not realistic for some average LULZ gangs to defeat the CAPITAL of a multi-city alliance with ease. The city has a population of thousands and how many players are in faction gangs??