No, these developments won't lead to vehicular gridlock in area. The main thing about the Skyway and mass transit that is being overlooked in the Brooklyn discussion the economic development component and its relationship with the overall strategy to bring vibrancy back to downtown. We're never going to have a truly vibrant pedestrian scale downtown district if we continue to ignore the impact of mass transit connectivity between urban neighborhoods.
For example, when these Brooklyn developments are completed, they will become isolated zones of pedestrian scale activity. They have their own residential base, commercial components, parks and thousands of office workers literally across the street. However, that neighborhood alone, won't be large enough to keep its commercial uses (ex. restaurants, grocery store, pharmacy, etc.) open. Their actual market will also rely on the residential and workforce population from surrounding areas like the North and Southbank. Skyway connectivity, actually allows people to live in various subdistricts of downtown and have direct access to Brooklyn's commercial infill without the need to get in a car and drive the extra mile.
For Brooklyn, Skyway connectivity allows its residents to have direct access to cultural attractions, nightlife, employment centers, businesses, etc. in the Northbank and Southbank, without the need of driving. Ignoring mass transit connectivity with Brooklyn's developments pretty much means we're content on having new infill in Brooklyn compete with the rest of downtown as it's own isolated spot of urban activity. It also means, we're perfectly content with them not helping one another work together to advance the concept of urban livability in the core.
This doesn't make a lot of sense and is quite the opposite of the goal to revitalize downtown. Heck, having to drive to the grocery, despite staying in some location like the Carling or Strand is the exact opposite of why people are generally attracted to urban living in the first place.