Two back to back torture cycles with the aim of breaking Lex's spirit should have had a compounding effect, wearing his mind down to its absolute limit. In truth, Lex could not claim that he didn't suffer. In fact, he suffered quite a lot.
The key factor contributing to Lex's suffering was not the agonizing, never ending pain of his own soul devouring itself repeatedly. It was, instead, not knowing when it would end. The Prison of Gluttony torture cycle had not been entirely forthcoming in describing the torture cycle, like the Crucible of Karma had.
This cycle also secretly affected Lex's perception of time, so what Lex felt like months or years was, in fact, mere hours.
The very fact that the previous torture cycle had, more or less, accurately described the torture he would endure was specifically designed so that he would believe what the Prison of Gluttony told him, thereby extending his torture greatly.
