That article's lede obviously didn't age well. However, I have had the article for many months and it doesn't read nearly as mistaken as one might suppose.
In a nutshell, the Rand author(s) noted all of Ukraine's disadvantages such as having to cover large rural areas, old equipment, and inexperience. He also noted Russia's experienced troops and pilots fought in the war in Syria, it had tactical fires cued by drones, and 'far better trained and equipped to conducted air and land warfare maneuvers. He said:
In short, the military balance between Russia and Ukraine is so lopsided in Moscow’s favor that any assistance Washington might provide in coming weeks would be largely irrelevant in determining the outcome of a conflict should it begin. Russia’s advantages in capacity, capability, and geography combine to pose insurmountable challenges for Ukrainian forces tasked with defending their country. The second argument for aid—changing the course of the war—thus does not hold water.
The third argument for aid is to provide assistance to enable a Ukrainian insurgency to impose costs on a Russian occupying force. Many have in mind the historical analogy here of U.S. aid to the mujahideen in Afghanistan following the Soviet invasion in 1979. Indeed, some are even recommending providing the same Stinger shoulder-launched anti-aircraft missiles that plagued the Soviet air force at the time. ...
If Russia attempts a long-term occupation of areas with lots of hostile Ukrainians, these forms of support could, on the margins, complicate matters for Moscow. But ... the prospect of a marginally more costly occupation is unlikely to make a difference to Moscow if it gets to that stage (of insurgency); it will have already absorbed far more significant costs. ...
Obviously the author did not forsee that the Russians would be unusually incompetent and their added "experience" far less advantageous. And the Ukrainians turned out far more skilled, than he imagined. Nor did he appreciate that it would develop into a bloody and costly stalemate (so far) of both sides and then cost Russia so dearly. On the other hand, while weapons have determined the military outcome of present, and the war has not become an insurgency, it's costs are "disproportionately borne by Ukrainians. (and) At that stage of conflict, thousands—or, more likely, tens of thousands—of Ukrainians will have died. [/quote]
He was somewhat correct, except all has happened before it is an insurgency and while he was also correct that the US would not likely not supply the weapons needed it has supplied more than he imagined which has checked the Russian advance.
He concluded: "Military assistance now will at best be marginal in affecting the outcome of the crisis. It might be morally justified to help a U.S. partner at risk of aggression. But given the scale of the potential threat to Ukraine and its forces, the most effective way Washington can help is to work on finding a diplomatic solution.".
Thing is, that too was also going be unacceptable to Ukraine in that the only "solution" Putin wanted was turning Ukraine back into a vassal of Russia's run by handpicked Russian oligarch's and a "mini me" state.
Western weapons have made a near term difference, and severely damaged the Russian army. But in the long run? That remains to be seen...