Pea! Hi! I used to go to University High before I moved schools, so I can give some insights into the extracurriculars available when studying at EBSS (I'm not too knowledgeable about the actual EBSS program, sorry!). Basically, EBSS is practically an extension of the Unihigh campus, so even though it's "select-entry", they are in the same space and thus share programs with Unihigh, I'm pretty sure.
For leadership & ECs, there is the SRC, various clubs like Debate club, crocheting, book club, maths/science, etc., and opportunities for sport as well as to join the school musical. There were quite a few events/charities that the leadership team runs which were pretty fun. I think it really depends on what school you go to, and since Unihigh/EBSS technically isn't a full selective school, there will still be people who aren't quite education oriented.
HOWEVER, my experience there was definitely positive. There are those who are, like yourself, ambitious and ready to put in the hard work to succeed, and once you find that group you can really build strong bonds and support each other. The school itself is big, with lots of dedicated study spaces, especially the EBSS building which is really new. The teachers are also overall pretty good: the ones I had were extremely enthusiastic about their subjects.
Hope that helps! Feel free to ask any more questions about the overall school/experience 🙂