Too bad you had a bad experience with your dev, but seriously, you just picked up css, people have been fighting it for years because of browser support. There's a reason why there are css reset stylesheets, and frameworks out there. If you are using it in one project great, but when you do it for living you will ended up building your own framework if you are not already using one. SASS also saves you so much time in development.
Yes, one of the issues with people who've recently learned the 2020 version of JS/CSS/frameworkX is that they assume what they've learned is the correct way to do things according to "the best, latest standard". It's a variation of Dunning-Kruger almost.
As you said, experienced engineers have been dealing with CSS browser support issues for years, so as a habit try to avoid using the latest shiny new features.
Also, experienced engineers do refresh their knowledge from time to time, but you might have caught them between refreshes. Remember that these engineers are also working 40-60 hours per week producing work output in addition to periodically refreshing their skillset. And depending on the environment they've worked in previously they may not have had the ability to use the latest features of whatever technology. Maybe they were working on a legacy app that didn't support ES6, for example. That would be less common now in the days of Babel, but there was a time a few years ago when it would have been reasonable for a working JS engineer not to be familiar with every detail of ES6, as an example.
