He cited the Customizer as one example where one is now very hard-pressed to find a theme developer who is rolling their own options panel after the Customizer was introduced as the new standard.
I think this is not the best example, because in my company our clients never ask us to make theme options with customizer, this is not always convient for the client and it's a lot more easier to make theme options panel with Advanced Custom Fields, for example or with the Redux Framework.