I think that if you stick to the 6-8 encounter adventuring day guidelines, that 5e is more challenging than 4e was, sticking to its adventuring day guidelines. However, 5e really relies on that attrition model to deliver a fair challenge. Bounded accuracy makes it easier than ever for PCs to punch above their weight class, so it becomes far more difficult to challenge a party with a smaller number of higher-CR encounters. You can kind of do it if you go well outside the encounter building guidelines, but that can lead to very swingy difficulty, where every fight you’re either bug or windshield depending on how the rolls go. On the other hand, I kinda think you’re “voiding the warranty” so to speak if you ignore the 6-8 encounter adventuring day guidelines. I think when run as designed, 5e is more challenging than 4e when it’s run as designed.