Hi!
I have few notes about the new functionality:
1.
This is what the Changelog says:
[Layout control] will automatically switch the active tab to the breakpoint you’re currently viewing in the builder. You can of course switch to any breakpoint you wish to style at any point, but this helps to ensure that you’re starting your work on the breakpoint you most likely intend to be updating.
That is not entirely correct. I work on 15’’ Laptop, and the open sidebar puts me into the 980PX-1199PX by default, while I am actually editing the 1200PX & UP breakpoint. This can easily be overlooked and and it is hard to get used to switch every time the Algorithm incorrectly assumes what am I editing. 
2.
Up until now the default reflow to the single column was at 481PX - 767PX. Now it is at 768PX - 979PX. I don’t think this is good thing to do. It is too early for the single column at this breakpoint and many old users used to the old way may start having broken layout simply because they don’t check this.
3.
Since the starting breakpoint was at 980PX-1199PX on a 15’’ laptop, whatever we make there, we have to re-make at the 1200PX & UP, [Edit: only if the layout is set to custom] and probably also at 768PX - 979PX, every single time. This is a lot of unnecessary work, in my opinion.
Here is what I would do:
There are only two logical Layouts, that are used in most cases. Probably over 95% of cases actually:
- Desktop—with whatever we have here. Let’s say a two column layout. We usually want it all the time no matter the viewport width, until too narrow so the Mobile has to kick in.
- Mobile—which is in most cases a single column that starts at 767PX.
Based on that, if we are forced to create a layout for several widths each time, it is time-consuming. So the logical approach would be that we always start on the full desktop width just like it was the case until now, and whatever layout we create there, it should cascade down until the mobile view starts. And the mobile view (single column) should start at 767PX just like before.
If sometimes we need special layouts, we can then easily change for any breakpoint, which is fantastic.
I see that cascading may be hard to pull-off so another approach may be to have only Desktop and wider Mobile by default, and then toggle on the additional ones if needed. Whatever the approach, the point is that we should avoid unnecessary repetitive work.
Off-topic:
Mobile view is still too wide. It is great as a breakpoint, but as a preview it is not usable, as the realistic preview starts at 360px. This is resulting with Headings that are sticking out and other design mistakes. I see those mistakes all the time done by X/Pro users who don’t check the design on the actual phone or in the browsers mobile view.
I think that the Responsive preview on the top should have a smaller button at the right side of the Mobile brekopoint preview, which would put the preview in 360PX width. It doesn’t have to be a breakpoint, just a “true mobile” preview.
Thanks!