She's right, that is the current trend in scholarship. This comes from Rosenstein's book on Roman Warfare. Here is the BMCR review.

Rosenstein is reacting to the traditional narrative, which all the ancient sources endorse, that runs something like this: Rome's military depended on soldiers of a certain wealth, who could afford to supply their own arms and support themselves on campaign. Classic citizen-soldiers. As Rome expanded, it gained access to more and more slaves. Slaves provided cheap labor that allowed industrial farmers to buy out the small farms that supported the mass of Roman soldiers, who were letting their farms go to seed through long overseas military service, instead of returning home after every campaigning season to tend to the farm. Losing their farms and no longer being eligible for military service these men did the only thing they could which was move to the city where their vote at least might buy them a grain dole. That's the traditional narrative.

Rosenstein's argument is that a) there isn't archaeological evidence for latinfundia in Italy (if I remember, he does find evidence for them in Sicily), and that there's no need for the troop crisis of the 2nd century to be a shortage of actual male bodies of military age and wealth - from comparative evidence it's perfectly clear that women can run a farm as well as men can.

So the conclusion is the crisis was made up; either honestly or for nefarious purposes by Ti. Gracchus.

It's a convincing argument - I've written about it before here. The real problem is it requires throwing out literally ALL of our ancient literary evidence, which just feels icky. I've been hashing this over for years and I'm slowly coming around to Rosenstein's side, slowly.

So Beard is entirely correct in her assessment of the field.

As to where the Gracchi got their support, well, they didn't get enough of it, did they?

As /u/Tiako has said before on several different threads, archaeologically there's little evidence for this sort of thing--if anything it appears that small-time farmers actually increased. Technically speaking latifundia are a phenomenon of the Principate--our first clear reference to them is in Pliny, and the OCD concludes based on textual evidence that they are a feature of the Julio-Claudians--but the large estates that Pliny describes must've existed in some form during the late Republic if they existed in his time, as we are told of massive private holdings of the ager publicus as early as Cato. Part of the problem is that what exactly a latifundium is is a bit unclear (the OCD gives several proposed definitions, ranging from landholdings above 500 iugera to the slave-staffed ranches that Pliny seems to be alluding to), but the fact of the matter is that our archaeological and literary evidence don't seem to line up. Personally I'm more than a bit wary of simply discarding something that has so much textual authority, but it's a problem that's still being discussed and debated. In fact, almost every aspect of Pliny's latifundia are debated. Pliny says that the latifundia are ruining Roman agriculture, but what he means by that is unclear--the OCD notes that in some interpretations Pliny doesn't mean that slave-staffed villas were pushing peasants off the land but that peasants were being hired in greater numbers by private landowners, ruining the slave estates of Cato's day. There's quite a lot of controversy about the whole affair

I'd add that the role of the popularis has everything to do with his methods and nothing to do with the actual content of his legislation. The Romans called someone who relied directly on the support of the citizen assemblies rather than first on the senatorial class a popularis, but a popularis did not necessarily have to propose "popular" motions, that is legislation that directly benefited the people as a whole. For example, Cicero shot down Rullus' proposed agrarian bill in the guise of a popularis, by appealing to the people for support against the bill instead of the senate. The tactic worked and Rullus' bill was knocked down, despite the fact that at least in theory it would've been beneficial to the majority of the people voting against it. The Gracchi are generally considered to have been quite conservative (they were both, especially Gaius, staunch aristocrats). Tiberius' land distributions, for example, are generally considered to have been intended to maintain, rather than reform, the existing property classes by maintaining the classes propertied enough to serve as soldiers (it's been suggested, by Rosenstein, that the problem Tiberius was responding to was not the loss of a propertied class but simply their unwillingness to serve in the army). What made Tiberius a popularis was not his legislation (indeed, the Gracchi actually passed laws that hurt the people as a whole, including Gaius' motion to limit the powers of the tribunes) but the fact that he brought the bill straight to the citizen assemblies without senatorial review, and then proposed the motion anyway even after the senate, having insisted on reviewing it anyway, voted against the motion. There was nothing wrong with that (the senate had no power legally to pass laws, and the senatorial review legally was supposed to be simply advisory) but it ticked off the senate. Tiberius' actions do not necessarily imply overwhelming popular support, they just indicate that he went against the direct desires of the senatorial class, although both he and his colleague (and opponent) Octavius violated the mos maiorum at several stages of the proceedings. What exactly was going on with the Gracchi, and in particular who supported them, is very much unclear, and the squabbling between the two tribunes would indicate that there was a great deal of division within the general population--this thread discusses some of that stuff in better detail

As a followup, what is in general /r/askhistorians opinion on this book by Mary Beard ?