I don’’t believe that’s the same though as you have basically 2 full width rows. You added an extra wrapper to achieve this so items 2 - 6 are separate grid items as such.
With flex you can keep them all as siblings and just set the h1 to flex:1 0 100%.
There was talk of adding a span all for the implicit grid to cater for auto columns but I don’t think it’s got anywhere yet. Otherwise you have to use the explicit grid columns which are not then auto width.
In cases where there’s not a relationship between column and row then flex is usually the best tool.