I actually find the Vocab easier most of the time, especially the Kunyomi seems to be quite easy to remember for me sometimes. Maybe because the Kunyomi is more unique than the onyomi in a lot of words. Also I know quite a lot of the more simple vocabulary already, so that makes it of course easier for me as well.
Talking about another approach to remembering vocab / kanji: Once I remember the meaning of a kanji by heart, I tend to “forget” the radicals used within it. I think at some point it seems more natural to make a link between the Kanji and the Vocab and vice versa. So sometimes I will be able to remember a Kanji reading (or meaning) because I know a word where it is used in or I will be able to remember / guess the reading of a vocabulary because I know the Kanji. I would think of it more as a circle of referencing rather than a one-way street of mnemonics.
Most important is I think to actually use the words. Reading the example sentences, getting a feeling for how the words are used. I think sometimes we focus so much on learning more and more Kanji and not actually using the words that we know. I think if you try to keep using the words / reading them, you will get a natural understanding and at some point know the words without having to use the mnemonics repeatedly. Having said that, in my opinion especially the gap between knowing the Kanji and knowing a compound-word seems like the last 20% you have to do, while it also helps you “consolidate” the Kanji you already know. But that’s just my personal experience. Would be nice to hear some other people’s opinions.
Anyways, I wouldn’t worry that much if you are just starting up. Once you get a better feeling for the language it will naturally be more easy to remember the vocabulary, especially if you saw one word or another somewhere else before or realize it popping up everywhere suddenly you learned it here.
I am from Germany and probably started learning Japanese like 10 years ago, on and off for the most time. I would say my understanding for smalltalk in Japanese is quite sufficient, but anything that goes beyond that my vocabulary understanding is really not enough, which is why I started WaniKani again. I once came until level 9 like 7 years ago, and then quit for some reason or another. I recently starting to get motivated about improving my Japanese again, and so far it is really going well and I am having a lot of fun.