This from the recently published Tolkien's Library. It is interesting, perhaps, to speculate on why Tolkien did not like Dune--though I think that's a slope down which we'd have to tread very carefully, considering he very clearly does not say. I do think it's especially fascinating that Tolkien states so matter-of-factly that he and Herbert are working "along the same lines", however. I'm not sure I'd have assumed that, initially.
Anyway, I hope this doesn't come across as click-bait or trolling. My interest here is largely sparked because I enjoy both authors so much. (And I have to admit to taking some enthusiastic strides down the aforementioned slope. I don't feel confident enough in my speculations yet, but the speculating is very fun.)