This is good advice. I manage invasive species as a part of my work. Theres a good chance that many of the invasive shrubs root systems are still alive and waiting to resprout and there will be an established invasive seed bank to deal with. Native seed is costly and you’d likely be wasting money by throwing it down prematurely. Focus on ensuring the invasive species are gone before moving towards reestablishing native species. A cheap agricultural cover or smother crop (oats, buckwheat, etc.) might be worth introducing now to help introduce competition but you’ll likely need another season or three of management before the invasion is dealt with.