I adhere to the 5-7-5 syllable scheme, because... well, I was taught that when young and I'm too old to change. The key idea is "do not waste even a syllable".
So, my opinion is that:
- A haiku should Have 3 very short lines; personally, I'm stuck on 5-7-5.
- It should meld two discordant notions and
- Say something that has never been said before.
- Big bonus points if your second line applies clearly to both your first and your third lines, very cool.
- Topic doesn't matter. Be you.
This is my personal opinion, not a scholarly attempt to answer the question. I understand that in English, we can say a lot more in 17 syllables than they can in Japanese. Regardless, the idea is to say a lot with a little. Make the reader think.