The claim being made is Mariupol will change how we approach urban warfare in the future. But the US and Europe have been involved in a lot of urban warfare since the 90s on. I don't know why Russia being nuts suddenly changes everything.

The difference is that Russia has really struggled.

And the Ukrainians, who have a rich history of manufacturing weapons, etc. have shown some extremely interesting defensive techniques, many of which would qualify as novel.

The heavy use of drones is the most dramatic example of that.

That being said, the article undercuts itself in precisely the way you’ve mentioned since it recognizes towards the end that urban warfare is not new, and further old school methods work as well, if not better, than newer tech.