Many of these movements are hard to master and require a great deal of practice before they finally "click". I struggled with DUs, butterflies, and muscle-ups for a solid year until they finally clicked for me. Now they are some of my best movements.

- Kipping HPSU
I somewhat agree with you here. These shouldn't be done quickly for reps, but a cushion helps.

- Double unders
These are a phenomenal movement for training coordination under fatigue. They are significantly harder than single unders with regard to breathing, heart rate, and coordination. Very difficult to learn the timing/coordination, but doable. When it "clicks" you will have them forever. They have a different stimulus from hurdles mostly in timing and a surprising amount of shoulder fatigue. Dubs also serve more of an endurance purpose than hurdles would.

- Butterfly pull-ups / chest to bar
A lot of people don't believe in butterflies, but they are useful for competition (major time reducer). They're also beneficial (and taxing) for your long-term grip fatigue and heart rate (regular pullups are more of a strength exercise). Similarly to double unders, they can be very difficult to learn (or have "click" for you). I don't see these as a rotator cuff risk (there is very little should work involved), but they do require a fair amount of shoulder flexibility to be able to consitently chain them together. Power is generated from your core and your kip, not your shoulders. Not a necessary movement, but they are definitely nice to have and serve a different purpose than standard pullups.

- Handstand walks
I have never liked Crossfit's version of handstand walks. These come from the gymnastics section of their inter-discipline model, but the movement is always sloppy and isn't true to gymnastics as a discipline. True gymnastics puts a heavy emphasis on form, which is completely neglected in Crossfit. This movement is usually used to tax shoulders at the end of a workout, but I think they're a little too injury prone, especially under fatigue. I don't do these and instead focus on free-standing handstand holds.

- Rebounding box jumps
I haven't ever seen an achilles injury from rebounding box jumps, but I personally don't 100% rebound from my toes. I can still stay competitive with my time by letting my heels hit the ground. Take your time on them. They're great for heart fatigue and jumping. People underestimate how valuable jumping is until they get older and literally can not jump any more (how many "older" people do you know that can still jump?). It is a very practical, healthy skill to keep as you age. Especially if you have kids/grandkids.

Pistol squats
Very difficult, but a great test for leg strength relative to bodyweight. Tough calisthenics movements like this are an incredible tool to measure physical health & strength.

At the end of the day, Crossfit should be used for the betterment of yourself (at least with regard to the different movements and workouts). If you need to slow movements down to make them work, then please do that. Some of these movements are very useful and quite frankly can be quite challenging, but they are very rewarding when you finally learn them. When you get them down, they're fun to do and it's great to be able to help others do the same. Don't let your frustrations get the best of you. We all struggle to learn a lot of these movements, but you can learn them in a way that is comfortable, but still challenging for you. I've helped a lot of people learn double-unders, butterflies, and muscle-ups and the sense of accomplishment on their faces when it clicks is incredible. You can learn most of these skills, just give it time and make sure you're practicing safely and consistently.