From my perspective I believe when you completely find comfortable with strong Basic understanding(HTML,CSS,JS) and not willing to reinvent the wheel and do things in a short period of time, then you are good to go with dev tools.

Interesting psuedo classes: nth-child(even),nth-child(odd),nth-child(2n),nth-child(2n + 5)(5-item position),only-child.

I agree with your point.These tools actually good for an individual, But I don't think much suitable for large organisation or complex projects. In large complex sites many front end dev and back end dev will work together simultaneously and they use git for future upgradation.If you need to modify even a small change in the code that the tool has produced its only possible for coders and some times it may be complex too.Finally these tools are not bad and they are improving so much. Currently they are not harmful to front end dev may be in feature they may ...will...

These tools are built to make a simple website without spending time on coding(or people who don't code), It does its job nicely. But when you want more customisation then these tools set back.

I too initially felt the same but after certain period of time i got changed my mind.Certain websites that designed based on Material Design looks Neat and pretty.Look over these sites(www.stamplay.com www.nimbusnine.co)

I personally prefer to use Bootstrap. It help you to develop the site much faster and responsive. I believe Every Front End dev will have knowledge on HTML and CSS so they can develop a site with out any framework. But the reason behind using framework is it reduce the development time and avoid redundant work.