I have been using Anki mainly to learn vocabulary, but I did use it for about three months with RTK before starting WK. Does WK feel more efficient? No. With Anki you can set yourself as high a learning load as you want and you can theoretically have it do everything WK does and more, including showing you visually similar kanji, managing leeches, and all the other stuff WK can do with the help of user scripts. For me, the advantage of WK is more that of convenience – you have everything set up for you and you just have to show up and do the work.
However, WK’s “inefficiency” also allowed me to focus on other things like immersion, grammar, and vocabulary, as the workload is quite small for a while and pretty manageable at the middle of it. At the end, though, there were a bunch of fast levels that led to me doing nothing but reviews day in and day out. This was completely avoidable and entirely my fault, as you can set the pace yourself by the number of lessons you do, but, like Anki, WK also easily lets you shoot yourself in the foot, if you’re not careful or focus more on going fast than actually acquiring things.
When I started over with WK, the mnemonics didn’t pose a problem for me, because I mostly made my own. Sometimes I took inspiration from WK’s stories and component names, but most of the time I simply went with what was more memorable for me. The way you learn the items on WK is wholly up to you. The only constraint is that WK is focused on recognition/comprehension, not recall/production, so that will have to be practiced separately, if it’s important for you.
After I finished WK, I’d say there were about 1000 kanji I remembered well most of the time, about 500 that I frequently misread or mistook for another kanji, and about 500 I was quite bad at, maybe occasionally got the meaning or the reading right. The reason for it, I’d say, was that I didn’t really read enough books. I only really started that after WK, as my reasoning was it would be much easier, and while that was definitely true, it also hindered my learning, I’d say. For kanji to really stick, you need to encounter them frequently in many contexts. First, the repetition itself helps solidify them. Mnemonics can help you recall or recognise something, but you need to get to a point where you just instantly know things. Secondly, sometimes when you learn something in a particular context, it is more because of that context that you remember it, so just something as simple as a different background or a different font might throw you off (there’s a script in WK, btw, that changes up fonts). Thirdly, you are able to much more easily form connections and make things memorable when you have some actual knowledge about Japanese and Japanese culture.
As for my advice… On one hand, it could be that reading practice might do you a lot more good than refreshing your knowledge with WK, especially as you have already learned a large number of items. Maybe try taking part in one of the book clubs here at the forums, for example. On the other hand, starting anew with a somewhat different system might help solidify existing knowledge and change up the way you’ve been learning things, helping you to break through the rut. Falling into a routine of course helps, as you do need to put in a large number of hours in language learning and nothing is more effective for that than regular engagement with a language, but it can also be demotivating and prevent you from taking a step forward, as you tend to cling to the same comfortable things and as a result feel as if you’re not making any progress, since you’re doing the same things over and over again. On the third hand, maybe you just need to shake up your existing study routine. These 10% of complete leeches that you mention, if you have such a hard time learning them, do you really need to? Maybe spend your time instead on things that you can learn more easily? And for those items that you already know well, do they really need to be in Anki? I realise that it might be difficult to throw away things you’ve painstakingly accumulated over a long time and worked hard on, but are they not just means to an end? That is, to learn Japanese, not to acquire a large Anki deck.
As for me, I’m doing a second round of WK alongside with ramping up my reading practice, because I feel like it’s more effective than doing either of them alone and that they tend to reinforce each other. But I’m also varying things up, from time to time. SRS is just one tool in the toolbox after all. I might read books intensively for a couple of months, but after that I might focus more on listening podcasts or watching shows with Japanese subtitles or doing speed reading practice or shadowing or studying with a textbook or translating. And I’ve found that if you set yourself priorities and focus on them for a short period of time, you also tend to see a more immediate improvement and it helps you to stay motivated. Here’s a somewhat lengthy video on this topic that inspired me: https://www.youtube.com/watch?v=eT7dx52wIC8
) , and a community to commiserate with. It’ll probably be a cinch as well given your existing experience. It will take a heck of a lot of time though, not going to lie.