Are Gen 6:11-13 a good example of repetition across toledoths?

Yes, because not only does it repeat themes brought out not long before—in a way that might well seem tiresome to a casual reader, or an indication of different sources, to a skeptical one—it is a highly germane elaboration. In other words, each “these are the generations of” sections marks a new beginning, and there is often blatant repetition across them. In Gen 6:11-13, the text reiterates the corruption of the earth (meaning mostly, but probably not only, the corruption of man), adding here that the earth was “filled with violence,” which was not specifically mentioned before, but it is certainly a natural consequence of “mighty men” (6:4) full of plans springing from “evil” thoughts (6:5). Verse 12 adds that God specifically took notice of this corruption, a repetition of 6:5, but adds that “all flesh had corrupted his [i.e., God’s] way upon the earth.”