Grid and Flex serve different purposes for layout. Also Grid has many of the same keywords as flex, but is more complex.
I find CSS Grid easier to understand than Flex. I also think it's easier (arguably more logical) to start with Grid and then understand Flexbox and how fits in your Grid.
The problem is that popular frameworks like Bootstrap and Bulma still don't support CSS Grid (they use flexbox only for layout, although Bootstrap 5 has opt-in CSS Grid). You could argue that CSS Grid makes frameworks redundant for layouts only.
Developers have rightly complained how cumbersome CSS layout has been in the past. It's ironic CSS Grid is available in all modern browsers but developers still aren't using it.
Not sure, but grid seems to be not very framework-able. Bootstrap frees you from choosing geometry by traditional grid system where you just class-mark columns and that's it. CSS grid is a whole new ~sublanguage that you have to master.
I find CSS Grid easier to understand than Flex. I also think it's easier (arguably more logical) to start with Grid and then understand Flexbox and how fits in your Grid.
The problem is that popular frameworks like Bootstrap and Bulma still don't support CSS Grid (they use flexbox only for layout, although Bootstrap 5 has opt-in CSS Grid). You could argue that CSS Grid makes frameworks redundant for layouts only.
Developers have rightly complained how cumbersome CSS layout has been in the past. It's ironic CSS Grid is available in all modern browsers but developers still aren't using it.