I completely understand your frustration, and I most definitely recommend installing the Double Check UserScript. It’s a little baffling to me that this is not a default feature of WaniKani. As a non-native English speaker, it’s sometimes extremely difficult for me to remember the specific English word that WaniKani expects, so as long as I’m able to understand to correct meaning I’ll consider it a pass.
Also I have some time-sensitive goals in mind so for critical-path items (if you don’t know what I’m talking about please let me know and I’ll elaborate!) I’ll be much more flexible with what I consider a pass. For example, if I forgot a prolonged vowel or mixed it up with the alternate reading, or even if I remember the overall meaning, I’ll pass the item. The retention improves as the kanji is used in vocabulary, and after clearing up the critical path I’m free to fail it and take as much time as needed. I only ever fail a critical-path item if I really don’t have any idea of what it is talking about (and even so, sometimes I just need to try again a couple of hours later, after taking a shower, to get it right).
The main thing you need to have in mind when using this approach is that the potential for burnout is considerably higher. At any given time you’ll have much more stuff to memorize and many more lessons. Retention is greatly improved at a slow-paced, stress-free progress. I actually intend to switch gears once I complete my current goals, which should happen by the end of the year.