> ...discredit any doubt I have in these extraordinary claims with underwhelming evidence.

Something unfortunate about our media environment is that science news is a dumbed down summary of a dumbed down summary of a dumbed down summary. These issues you're flagging, a lack of evidence and overstated certainty - they're an artifact of the reporting process. If you work your way back to the original sources, there will be a heck of a lot of evidence and it will carry error bars (so the certainty is precisely & appropriately stated). There's bad or even fraudulent papers out there but there's a huge amount of good science being done by honest researchers who are just as concerned as you are about the quality of the evidence and the degree of certainty.

Eg, there really is a compelling explanation of how we can know the composition of a gas giant light-years away, and it isn't invented out of thin air, it's been 100+ year process of understanding spectroscopy and cosmology, building better telescopes, etc. It's the culmination of generations of scientists pushing the field forward millimeter by millimeter.