It does sound like you know quite a bit already if you recognize about half the level 50 kanji. Rest assured that others have also come in with a lot of knowledge and benefited from using WaniKani. For example: [Review] Making it to level 60 as an advanced Japanese learner
I’ve also been impressed by the many people who finish WaniKani in little over a year (I took about two and a half years). But many of those people spend so much time on WaniKani that they learn little to no grammar and don’t practice reading at all during that period. Of course, that isn’t the case for everyone that went fast, and others say focusing exclusively on kanji first worked well for them anyway. Regardless, it’s still impressive and I know I would never have been able to do it that fast.