lozlo It will simply be unfair for all parties. So what happens when the previous book warrants a low price for the next book? Should the translator/author simply drop it since why waste efforts working on something that you know will earn you lesser? For authors, it's a natural choice, but for translations, it will only lead to numerous books with translators just dropping it. Also the highly dynamic nature of it makes this problematic for some translators. Some of them are living paycheck to paycheck on the work they do. Doubt people would like that.
Also the reason why word count is used is because that determines the amount of time you need to work on the translation of that chapter. If it's all the same or based on some dynamic pricing system, what happens when a translator encounters a 15,000 word chapter (I've faced that before)? 5-6x the usual work for the same pay? It will very likely drop the release rates as there's so much inertia to work on something like that.
Translation quality is hard to judge. The readers generally rate very high ratings for all the translations. Even the shittiest translations are something like a 4.2/5, and the highest is somewhat closer to 4.9. When you only have a 4.2 to 4.9 range, it's hard to determine if it's really due to translation quality or not, or simply that some NTR or rape happened in the plot (and how are you going to determine which one is it when there are thousands of chapters produced by Webnovel translators every month?). 'Educating' the readers to rate properly is an endeavor that's even more daunting.
The current system is working okay. The grumblings are mostly from the verbal minority.