It sadly doesn't solve the problem with literally all and every grid generator out there - no proper support for spans and areas. The biggest power of grid is the free-form layouting it provides - it just gets lost in these simplistic editors.
The real power of grid is the features you speak of plus the alignment features. With this editor you have a long way to go to create useful responsive layouts with niceties such as implicit grids.
I am coming to the conclusion that you don't need a tool to make a grid for you, that knowing how to write the CSS is where it is at.
The problem is that CSS Grid is a new mindset, if you have been brought up to think in terms of things like '960 pixel wide' grids or how print newspapers do grids then you are not going to fully get it.
I also do not like it how this example perpetuates the div element. According to the specification the 'div' element is not to be used except for in a last resort.
The CSS Grid way of working means there is no need for div wrappers. Centering and aligning content can be done without the div. Again this requires new thinking and people used to slapping divs everywhere with a multitude of class attributes are still thinking they are working with a framework.
If you look at the code for the page rather than the generated code there are a few off-spec 'crimes' that are not needed with CSS Grid. The 'main' element should be in the 'body' as a direct descendent, with this page it nested inside a section that is nested inside a div. This is then styled with flex layout rather than CSS Grid. The page uses complicated calc hacks rather than CSS Grid. The document structure is also quite wrong, the side panel is not an 'aside' outside of the 'main' content.
For this page I would go with '1fr auto' to define the columns. The sidepanel would then take the space it needs and the grid take up the rest. No 'calc' sums needed in the CSS.
Now if you type 'auto' in one of the columns (instead of 1fr) then you get some patronising message saying "Must use real CSS units, goofball". The thing is that for CSS Grid, 'auto' is what you want to be typing once or twice in every project, not being able to use 'auto' (because apparently only goofballs do it) indicates to me that this is quite a beginner project with a lot more work needed.
CSS Grid enables you to strip out all presentational markup from a page, it can be pure content using the HTML5 content sectioning elements. This is a fundamentally different way of working than the hacks of the past. If you wish to further bloat hacky HTML then this tool will help you do it, it won't challenge ingrained attitudes and get people to the promised land of concise, unbloated HTML that separates the concerns.