I think comparisons between Rewrite and other Key works are legitimate. Despite Rewrite having significant thematic differences as well as a higher focus on action, I think it is still very much fundamentally a Key VN.
Romeo Tanaka’s presence is pretty clear - it’s obvious that Maeda wasn’t the main scenario writer behind Rewrite. Nevertheless, I think it’s accurate to say that Rewrite is essentially Tanaka’s style being poured into a Key mold than anything else. It’s still very much Key, but just with a different flair.
To start with, Rewrite still has a significant focus on character-to-character interactions, and the greater focus on action in some routes is just a slight deviation from what you’d expect of a Key character route - the routes are still essentially character driven romance dramas more than they are anything else. I think the action and fantasy elements of Rewrite might make it more appealing to those who might not ordinarily be so inclined towards a Key VN, but there’s not enough of it there to change what Rewrite fundamentally is.
Even in routes where events of catastrophic proportions occur, the focus is generally on how those events impact Kotarou and the chosen girl and their emotional states rather than on the events themselves. To put it another way, I think Rewrite is basically a character drama where the fantasy and action elements are there to provide the basis for said drama, rather than a fantasy/action VN that just happens to have some character drama attached.
As previously mentioned, Rewrite still adheres to what you could call the typical Key formula, and of course on a production values basis it’s similar to previous works in terms of artstyle and what you’d expect of a Key OST.
I think the real major wrench in the comparisons between Rewrite and what is typically associated with Key is Moon and Terra, where Rewrite just kinda goes totally off the wheels and basically becomes almost purely a fantasy/action VN with some of everyones favorite Tanaka pithiness strewn around everywhere. I still think Terra on a surface level is basically similar to the concept of Clannad/LB “true routes”, but reading it feels very different.