You seem to find it very easy to dismiss the works of one of the greatest literary scholars of the 20th century.
His academic work may have been very good and may still stand up, for all I know. Or maybe not; it's not my area, though I do know these things can be superseded. I've read a little of it relating to the mediaeval troubadour tradition, courtly love etc. while researching for something else. It's OK. His Narnia books however are tenth-rate pseudo-Tolkien rip-offs and his apologetics risible.
Do you seriously think that Lewis did not realise what a non sequitur is?
Why not? Competence, even excellence, even genius in one specific field is not and never has been a guarantee of competence in any other. A bad argument is a bad argument whoever uses it. And Lewis can deploy bad arguments with the best - or is that the worst? - of them. Gordon's analysis, brief as it was, was quite correct. Lewis is doing no more than any business does on a daily basis; trying to tout his wares that he wants you to buy by rubbishing the competition. It has always been standard practice in especially monotheistic religions just as it has in trade and commerce.