I'm not sure what "over use" really means here, but I think calling it a mistake is wrong. Using bootstrap (or any other framework) is optimizing for something other than download size. That might be development speed, better design than you're capable of, cross-browser compatibility, etc, but it's not wrong unless you're building a site that really needs to be fast and small.

If you're building an admin page that'll be accessed by 5 people in total and can be cached for a year between updates then Bootstrap is great.

If you're building a blog that's going to get 2000 readers a month and want to concentrate on writing articles instead of writing frontend code, Bootstrap works really well.

If you're making a new login form for Facebook's homepage that'll get 100,000,000 visitors in the first hour it's live, maybe Bootstrap is the wrong choice.

CSS frameworks are tools, and they have their place. There isn't a universal rule that says using one is wrong.

That said, if the only part of Bootstrap you're using is the grid and you don't need the UI toolkit, then browsers have got you covered these days - https://developer.mozilla.org/en-US/docs/Web/CSS/CSS_Grid_La...