The author is engaging in a false dilemma, a false either/or dichotomy, ignoring any alternative to his assertions, for they presuppose a definition of good and evil - and in which which an omnipotent omniscient being must be the supreme judge - and being both willing and able to prevent evil does not mean that what is objectively evil cannot be allowed in order to work for good.
The presumption that a omniscient and omnipotent, just and merciful Being was unjust in allowing evil or in sending judgments presumes omniscience and omnipotence on the part of the one who is judging God (not that I am not guilty of that, at least as a emotional yet irrational reaction). For to be evil presumes that such was not justly warranted in the light of what it would accomplish, not simply in this life but for eternity. And only the God of the Bible knows what all the effects of even our next breath will be - not only for this life life but for eternity - and can and will make it all work for the good of those who love God, and thus the Good. (Rm. 8:28)
And an omniscient and omnipotent Being is able to accomplish His plan without forcing man to go against his will, as intolerable as that can be to some whose knowledge is less in this realm than a cave man trying to code a software program in dim light that would run the Pentagon which he never heard about.
Finally, God gives all that is good, and His command for creation to worship Him as the infinite omniscient and omnipotent being who cannot fail, is unselfish, for God does not need anything, (Acts 17:25) and to worship perfection is only right and to the benefit of man, who actually causes God grief. But rather than wipe man out again and again, God spared not His own Son to save us, and who himself loved us and gave Himself for us, that we may live thru Him, thanks and glory be to God!
I see you noticed the IS-IF thing; too.