Thats not entirely true. While you can achieve a better result using strips and staying in the grid, it only goes so far. No matter what you do, if you resize your screen the elements will never adjust properly and eventually the layout will break. You don’t see Classic sites switching between Desktop, Tablet and Mobile automatically.
The other big issue is someone can have the exact same size screen as you but if you have a higher resolution and they have a lower resolution screen, and you both load the site on desktop view, your views will be different. Having a fully responsive site means even a slight change in resolution or pixel size wont stop someone from properly viewing your site. On classic this is not the case.
You also run into the problem of not being able to fully utilize the entire screen because of the grid lines. Fully responsive sites like Editor X, WordPress, Shopify, etc. don’t have this constraint.