Except they completely bungled the war aspect. Cameron's original T2 script/ideas established that most of the resistance fighters were South Americans who'd had experience with guerrilla warfare, and were living in areas not targeted by the US/Russia nuke hits. Granted, T3 also seemed to get this wrong with that shot of the troops holding up a battered Stars and Stripes, but one could still imagine that most of the fighters just off-frame were South American.
Not portraying a script idea that was not established in any way in the first three films (including Cameron's two) is not "bungling" anything. Besides, the mix of ethnicity and language in the
T:S Resistance was not noticeably different from that of the previous films (with the addition of a Russian Resistance leader).
Furthermore, while the body count from a full-scale nuclear war would be truly horrific, if we go by
T:2 roughly half the world's population was killed in the nuclear war itself (three billion), leaving another three billion around that SkyNet had to round up and exterminate, hence the concentration camps with the barcode tattoos. So there would still be tens of millions of American survivors (possibly over 100 million) that SkyNet needed to kill and who would fill out the Resistance ranks, which was consistent with what was depicted in all the films.
And the notion that humans could build a heavily-fortified base not that far from LA that the machines knew about, but couldn't quite smash? Robs them of all their power. The human resistance movement should be a one-shot, desperate LotR-style invasion, not a protracted conflict with established human bases.
SkyNet was not based in LA in 2018, it was based in San Francisco and had a more defensive strategy while it consolidated its power. It moved its base of operations to LA to take a more offensive strategy after SkyNet HQ in San Francisco was destroyed in
T:S. Once it established air superiority over Southern California and started destroying Resistance bases there, the Resistance was forced to switch to primarily guerrilla-style hit-and-run attacks from the infrared-blocking safety of the underground sewer/subway system in Los Angeles itself, as we see in 2027, 2029, and 2032.
Also, it makes perfect sense for the Resistance to be much more powerful and equipped with military aircraft, ships, and bases only 14-years after Judgment Day, as opposed to 32/28-years later in the case of the first three films (relative to their respective Judgement Days). You'll notice their hardware is all falling apart and getting blown up daily in a war of attrition against SkyNet with its assembly lines and mass produced drones and robots. It's only a matter of time before most of the remnants of the military hardware are destroyed and all that's left are the soldiers themselves fighting in beat up cars or on foot.
T:S has a lot of problems, but the depiction of the Resistance situation in 2018 wasn't one of them.
