Nobody is saying that each tower on this stretch should be an icon in its own right, but only that nearly identical towers would create a soulless and visually unengaging neighbourhood. You rightly evoked the image of the many clusters of nearly identical slabs that we have all over in Toronto, such as on Davisville, among other places, but I don't think most people see these as being architecturally or urbanistically successful. Replicating such mistakes is exactly what I'd like to avoid.
Furthermore, 90% of the designs that we've gotten during this boom come from the neo-modern style and accordingly they'd all more or less be able to relate to each other in a relatively complimentary way, so it's disingenuous to claim that if these towers aren't identical, the only other option is a totally haphazard mix of styles from different era. If for example, rather than Casa I, II and II on this small stretch, we got Casa and say, something like Theatre Park and Charlie, I think that would provide a much richer visual experience without significant dissonance of style.