With silicon there are a bunch of issues. The bonds aren't as stable, so everything would have to be extremely cold, which makes chemical reactions very slow. Also organisms would exhale sand, which is not ideal.
Carbon and water are just uniquely qualified as a basis for life.
If you say life may be possible without complex chemistry then I'd be interested in your arguments. In my experience that line of reasoning boils down to "just because we can't imagine it doesn't mean it's impossible". Maybe, but I'm unable to discuss things neither you or me can imagine.
The fractional percentage camp is based off the observed spectrum. the most of it camp is based off observed material composition in the solar system.
Here is the stellar remnant theory. I found it a bit extreme, but fun to think about.
https://arxiv.org/ftp/astro-ph/papers/0410/0410569.pdf
Personally I would bet on the sun(as it is a second generation star)having a more substantial iron core than first thought, probably a quarter of the mass, too much iron, there would be no fusion, but it does not make any sense to me that as full of iron as the inner solar system is there would be negligible amounts in the center of the sun. Perhaps there is an unknown mechanism that prevents the iron from creating photons to sus out with spectrography(my guess is the thousands of kilometers of hydrogen around the core).
FTL isn't massless, massless means exactly the speed of light. Imaginary mass (as in multiples of the square root of minus one) would be FTL if such things exist.
If we’re not literally on the edge of the balloon is someone else looking back in time at us?
https://www.colorado.edu/ness/science/cosmic-dawn
The Milky Way in comparison was 14 BILLION years later (vs half billion)
Any life with a few billion years headstart over humans might have figured out FTL travel or at least FTL communication (massless)
adding: yup, I screwed up on Milky Way age vs cosmos age, cosmos roughly 14 billion years, Milky Way first stars roughly 1 billion years after cosmos started