But the last sentence is the issue under dispute, specifically whether the Hannibalic war necessitated the creation of private armies.
If Sulla, Pompey, and Caesar had not provided land to their veterans, their veterans would still have left service far richer than they had entered it. These soldiers had been paid for their service; they were given leave to rape and pillage the provinces at their leisure; and their commanders grew monstrously rich from their campaigns. So, there's no point in pretending that the soldiers would have faced starvation upon leaving the service. Moreover, in every case, the commanders you mentioned could have patiently attempted to purchase land out of their own purse for their soldiers. But they didn't. They relied on confiscation, proscription, and civil war to evacuate speedily those Roman lands they wished to disburse to their veterans. In short, Sulla, Pompey, and Caesar came to view Roman property holders in the same way that they learned to view non-Roman property holders--as de-humanized fodder for their own ambition. Sulla, Pompey, and Caesar weren't frustrated social workers--they were thugs who were accustomed to taking what they wanted, rights be damned.
What is the relevance of the Hannibalic war to these affairs? The connection seems very slight to me. If I'm misunderstanding you, please let me know.
The soldiers may have been far richer when exiting service, but they still had to eat and drink ten or twenty years ahead. Ager publicus was not something that you could purchase (not with a soldiers salary anyway) - it was lent to you by the republic and the republic in return demanded a small yearly fee.
The triumvires relied on proscription and confiscation because there was no land to buy - most of the ager publicus was already on the hands of the allies of Rome. This is exactly why Pompey, through Caesar, had the tribunate propose a landlaw in Pompeys favor.
The relevance of the second punic war to these affais? Well, I never wrote that the pillaging of Hannibal necessitated the fall of the republic - only that it catalysed the process. A great portion of the italic farmland had been destroyed and cremated by Hannibals soldiers, and returning from the final battle the roman/italian peasant only saw scorged earth. At the same time the price for grain had dropped quite a deal due to increasing competition from abroad - most respectively Egypt. With no other alternatives (as I wrote before: olives and caddle was expensive and needed starting capital due to the long wait for revenues) and in conjunction with the still richer aristocracy - who needed something to invest their capital in, since there was a law forbidding senators from taking up commerce - the roman and italian peasant had a natural strong urge to sell to the highest bidder. This was the beginning of the landless soldier and the proletarii.
I'm not claiming that the landless soldier wouldn't have come to be without the second ounic war, but that war certainly did not make things better.