I was the same boat with you except I did both Jap Sl and Chinese SLA plus other 4 sub in year 12.
I have a huge interest in Japanese and luckily I did have a very nice Japanese teacher at my school and wiling to help me with anything. My first language is cantonese but I do speak so-so mandarin and I have not studied it since year 6.
I'll say Chinese SLA is super competitive, saying that you are average (that is able to speak chinese without thinking too much in daily conversation) and if you willing to put effort in then probably around 30 range. But if you compare to Japanese, getting a 30 is easy (unless you are saying you are struggling think what to speak). And even with my level of Chinese
without studying (I have also miss a SAC), I have only manage to get 26 and even the native speaker born in China and have studied in China until year 6 in my school did not manage to get over 40. This is how hard it is!
And also, from my experience I will definite say Japanese examiner are really trying to help student to achieve high score, they genuinely are being nice to student and will not trying get the harsh way out of you while Chinese, they are trying to pick bones from egg (even in mock exam
) (Not saying all of them are but definitely quite a few exist)
But really, if you can do both then do both! Both of them do scale up a lot and it's quite advantage in Atar as they scale up a lot. But if you can fit both in then definitely go for Japanese given 99% SLA are either background/dialect speaker or student have been study aboard in Chinese region. And able to recognise Chinese character (even simplified one) already gave you some sort of sense in knowing or guessing the meaning for kanji and it's already a advantage over some student.