First point of complexity that's always being lost: power users aren't born, they're made - made from repeated exposure. First point of nuance being lost: being nice to power users means having features available and discoverable; it doesn't mean you have to clutter your pretty, simple, polished UX with it (and so decide to not do the features in fear of design impact).
Why it matters? Because operating a lot of hot, hip software - like Trello - ends up being a dayjob for many people. If you're sitting 8 hours a day, 5 days a week, for years, using mostly a single piece of software, you're in a perfect position to become power user of that product, entirely effortlessly. If that software is "pandering to power users", then your work speed, quality and reliability will keep going up over time, as you get more proficient and efficient at using the tool. Whether you'll use saved time to rest, to slack off, or to get more work done - that's up to you, but you have a choice, and your employer saves money (whether through increased efficiency or reduced risk of employee burnout). Meanwhile, if the software embraces the "simple use only" principle, you'll just be wasting your life in front of a glorified Fisher-Price toy.
"Power user friendly" really means "leaving space for users to grow".
"stupid people" is also a strawman. There are plenty of smart people out there who just want shit to work. They don't want to fiddle with everything like power users do.
Medical/healthcare professionals are a good example of this.
We built these empires. But then we get kicked out because stupid people are stupid.
Do we elevate these folks to power user status? No. Instead we stoop to their level, all in service of making more money.
Sick of watching tech (and people) functioning at a tiny fraction of their potential. We could be living in a beautiful world where people bend tech to their will, and not the other way around