Easy to customise frontend UI library

Thats comparing apples and elephants... In the video you show a complicated way of customizing MUI styles of nested elements with a specific state, however for mantine you only show simple style overrides directly to the component itself, this is similarly easy to do in MUI with the sx prop:

import { Box } from '@mui/material'
<Box sx={{ mt: 2, p: 1, bgcolor: 'primary.main' }}>Hello world!</Box>

In short, you're showing that MUI is capable of doing things that mantine can't do and you do not show that doing simple things in mantine is just as simple as in MUI