I have to admit I don't understand why one's feelings about Gervais are so impacted by whether Karl P. is a constructed persona or not. Is it because Tom has referred to Gervais' mocking a mentally ill person on those podcasts? I'm not sure how literally Tom meant it, but I had never heard that claimed about Karl Pilkington, so I assumed Tom was either hyperbolizing or just hadn't listened that closely.
Myself, I don't hate Gervais as much as some here, but I haven't had the slightest interest in any of his projects since The Office and the podcast. I'm not gonna watch Derek, but the thought of it making me "shed a tear" sets off my Jerry Lewis-dar a bit.