Yes, but not because they make CSS easier.
CSS was alway easy. All you had to understand is the box model and some basic HTML rendering caveats. Maybe browser differences, but there are pretty good lists out there for that.
I’m a developer. I create websites since 1998. I have really seen and did a lot. Yet, if you have no other choice but me to design your web page, you are doomed. I’m very bad at design. I know some color theory, I can mimic the look of some pages, but that’s pretty much it.
Frameworks, especially the ones that come with a theme or two, are my only chance. They give me basic elements to work with that look good together. However, and that goes for every framework, not just CSS: if you don’t understand a language, frameworks will cause more harm than good.