Part of this might be your expectations.
Why is almost anything I push to Master/Enlightened failing to stick?
This is definitely not true, though it may feel like it is. Let’s do some simple math, you have a total of 2,405 items combined between Mastered, Enlightened, and Burned. Even if all of your leeches came from this category, that’s only 339/2405 * 100 ≈ 14% of your long-term items.
14% isn’t too bad, this is equivalent to averaging 86% on your reviews, which most would agree is pretty alright for longer term material.
This is also a downside of a locked off SRS system like WK, you basically only ever see the stuff that is new and the stuff that you are bad at, thus reinforcing your perception that you’re doing poorly while all the stuff you’re good at quietly sneaks away to the burned pile.
When I feel down about my % retained on other SRS systems like Memrise I just run through my general queue instead of focusing on my difficult words and feel great plowing through 9/10 items without issue. It’s a pity that WK doesn’t let you do that, but perhaps you could KaniWani?