The author of the post you are responding to questioned the approach of relying upon paid testimony from self-selected defectors as an objective account of the DPRK as a whole. This is not irreconcilable with a critical view of the DPRK, and only indirectly addresses the point you are making here.

It is facile to observe that any form of society can 'produce a good life' for some subset of its citizens. You have not persuasively argued that conceding this point means agreeing to the bizarre equivocal statement that 'there is no reason to chose liberal democracy over totalitarianism.'