Extremely dependent on a number of factors, mostly hardware and configuration. I had a Thinkpad T480 and on a stock fedora install it definitely died faster than W10, but after setting up TLP and Powertop I squeezed ~2 more hours of use out of it than Windows could manage. Ditto for my framework 13, I get all day battery life on NixOS but when I’ve tested windows on it I lose a few hours immediately
Professional audits happen for big projects, and hobbyists audit the programs they use frequently. In addition, some projects adhere to the reproducible builds guidelines, which ensures the packages you’re receiving are identical to the upstream repo. There’s more work to be done in formalizing and automating these processes but this isn’t a major issue by any means