There's a difference between rigidity and difficulty. Memorizing patterns and executing them (especially on a training dummy) is not necessarily difficult, while being flexible in each moment-by-moment scenario often takes far more skill in most environments. I don't consider Castlevania 1 NES to be a very difficult game because I can beat it with no deaths due to memorizing it, but sure it's punishing for mistakes. A game I would say that's far more difficult is DQXI Draconian Mode where you really need to plan and react accordingly, so you can't just memorize and automatically succeed.
Of course difficulty is subjective still, but you don't comprehend that.
It isn't necessarily about being hard, but about it being fun or well designed. Remember less than 10 total PLDs/WARs worldwide could clear P8s week 1, and a lot of that I believe is due to this 2 minute design. DPS disparity has reached up to 15% in some cases. So not only are things less balanced than in Creator/SB/SHB, but most people (myself included) find them to be much less enjoyable.
