I can relate to stuff taking a while to stick and I definitely felt that way at the start. I found though that learning on here was a build up thing, with all previous learning as I went through building up.
I’d second the suggestion of note taking, not for every vocab item, but for any item you don’t get right in the first review season after learning, is my recommendation.
As far as speed goes, I wouldn’t worry about other people going fast, just worry about your own speed; this is a mountain climb, not a sprint. It’s also worth understanding that there’s a maximum speed in any case:
Given how the SRS (Spaced Repetition System) works, there is a maximum possible speed at which it’s possible to progress on WaniKani; 6 days 20hours per level.
That maximum speed is because you can only progress to the next level when you’ve gotten the majority of kanji for the current level to Guru. When you level up, you get just over half of the kanji for that level unlocked and you must get these up to Guru before you unlock the rest for that level.
So if you look at the maths this way:
Note that these intervals are reduced by around 50% for level 1 and 2, so they’ll go faster
Unlock Kanji = 0hrs
Apprentice 1 -> 2 = 4hrs later
Apprentice 2 -> 3 = 8hrs after that
Apprentice 3 -> 4 = 23hrs after that
Apprentice 4 -> Guru = 47hrs after that
So the total levelling time for first batch = 3 days 10 hours
You then unlock the next batch and must spend 3 days 10 hours again on those