I’ve not used containers much in recent builds either and I haven’t used rows since Flexbox launched. The div block with a max width of 1200 or 1500px gives a fuller look on a larger screen.
I always give the advice of learning to use Flexbox, it’s so much quicker to create and edit later on.
On your video, you’re editing the width of the flex wrapper with pixels at each breakpoint, which doesn’t really give a truly responsive design. On the desktop breakpoint just give a width of 100% to the wrapper and the content will resize automatically with the viewport width. Maybe you do this already though and just not on this video?
I think the way you set up near the end with the invisible spacer is a little complicated, you can do that without the spacer using purely flexbox with two inner wrappers 50/50 or 40/60 aligned horizontally, and inside those the objects would be stacked vertically.
The beauty of this though is that your way is NOT wrong at all, it’s like mental arithmetics… everyone calculates differently and as long as you get to the same result, who cares?