Wanikani still slow...even at level 6 (the issue is 'balance and spread' within a level...not predictability, nor the rate of upleveling)

It seems like a lot of your frustration stems from not understanding how the system works. Once you know how it works, you know exactly why you have (or don’t have) reviews at a given time.

I’ll try to explain how it works briefly: For each level, you need to get 90% of the kanji to Guru. Some of the kanji you need to Guru are blocked by radicals that you need to Guru first. So the fastest way through a level is to Guru the new radicals ASAP, and then Guru the kanji that use those radicals ASAP (assuming that by then, you’ll have Guru’d most/all of the kanji that were available at the start of the level).

Getting an item to Guru means reviewing it after 4, 8, 24, and 48 hours. You can try to time your reviews to get to the items on your “critical path” as soon as they come up. I find that it works best to learn items in the morning, so I can do the 4- and 8- hour reviews in the same day, or in the early evening so I can do the 4-hour review at night, and the 8-hour review the following morning.

Sometimes it happens that you fail a few too many reviews late in a level, and have to wait up to three days (for the 24-hour and 48-hour reviews) to get another crack at those items. It’s a bummer, but that’s life. After level 20 or so, such delays will feel like a break.

I’d recommend the Ultimate Timeline and Dashboard Progress Plus scripts. These will help you understand exactly what you need to do to finish your current level, and when your reviews are coming up: