Creditors owed identical amounts under identical defaulted Argentine bonds, including identical pari passu clauses, could get very different recoveries under the plaintiffs' theory of ratable payment--unless all such creditors are corralled into a mandatory class action that divvies up Argentina's surplus among them under equitable supervision of the courts.
Unequal recovery under identical instruments could happen if, for example, Argentina ran out of money after paying the first wave of pari passu litigants. The result seems out of whack with the original "Tom, Dick, and Harry" theory of the pari passu clause in sovereign debt instruments, as famously articulated by Professor Lowenfeld beginning in 1997 (this version 2000):
Suppose, for example, the total debt is $50,000 and the borrower has only $30,000 available. Tom lent $20,000 and Dick and Harry lent $15,000 each. The borrower must pay three fifths of the amount owed to each one -- i.e., $12,000 to Tom, and $9,000 each to Dick and Harry. Of course the reamaining sums would remain as obligations of the borrower. But if the borrwer proposed to pay Tom $20,000 in full satisfaction, Dick $10,000 and Harry nothing, a court could and should issue an injunction at the behest of Harry. The injunction would run in the first instance against the borrower, but I believe ... to Tom and Dick as well.