My idle times, browsing something like HN, or sitting in #emacs I get near 20 hours on my t450s and about 13 on my x220.
I think low low low idle power consumption is key to long infrequent charges. This is because the second you are not using your computer then it should also not be using power. For example, my t450s without adjusting the screen bigness idles at 2.8W, so tons of idle time with a 97WH battery.
You can't really optimize power for when you are using it. If you are compiling, you want the fastest compile time and use the most power. Same for other things that take power.
I go all weekend not charging my personal laptop and the only times I close the lid is when I am going to bed. Otherwise I leave the lid open, same brightness and walk away for hours and come back and continue where I left off.
So I see your point about people saying "I get 9 hours of battery life." doing nothing, but even 9 hours of doing nothing is fairly low, given I can make a 10 year old laptop get close to 18 hours, and a 4 year old one get near 21 hours "doing nothing".