I did strict KETO for 4 months. The first week was hell. But after that it was nice. My skin was clear, my brain was sharp and I was generally happy. Until I started working out heavy again. Soreness longer and more than usual. SO carb cycling works for me.

But it's not true la, you won't feel weak. If your body is highly toxic, you'll have keto flu for sure. I didn't have that because I generally ate clean and don't have a sugar addiction at all.

Funny story: perhaps looking at the blood test results (which  I did after keto), was pretty good.

1. You don't just eat crap fats all day lah. Please. fresh veges, healthy fats like avocado, olive oil etc.
2. Calorie controlled. Duh. Basic 101. Cutting calories.
3. My main problem was dairy and glucose. Spikes in my insulin caused my hormones to go whack, and I had bloodwork done beforehand to prove it.
4. Keto was advised by my GP, who said to do it clean. And i did. It worked for me when nothing else would. Also it pinpointed why I was having random skin break outs.All that's been solved.
5. When your body swaps it energy storage to fat... the glycogen (glucose) is no longer the main supplement.

What you are very confused about is: different stroked for different folks. Don't hate on what you don't know or perhaps never even experienced. It has health benefits for folks who do it right, it also has consequences for people who do it wrong.

Oh and I never had mood swings or carb cravings. What I had was initial annoyance of dryness in my hands despite drinking 1.5 litres of water. Once I doubled the water intake, all these solved itself. I was also able to sleep so well at night. Did not feel weak at all. In fact I was lifting heavier and running faster on days iI worked out. ONly issue was soreness was a little longer than usual when doing  new workout. But after reading up and gettign medical advice from qualified pros (aka the GP), this was solved.

Again, different strokes for different folks.