I agree.
For the loss of the pre-1950's urban fabric, I would blame the "carpet bombing of WW II Dresden" approach taken in the 50's and 60's for the destruction of the GC and Charles River Park areas.
One could say the same for the 1950's Central Artery project, but that was a relatively narrow scar compared to the other two mentioned above.
In an alternative universe, GC and Charles River Park would never have happened, and instead we'd have, at a minumum, a vibrant North-End type neighborhood in the West End, and a high-density mix of towers and low/medium rise buildings in the GC area. All the empty wind-blown "plazas", superblocks, and massive isolated chunks of concrete brutalism would not be there.
In a rational future, this will happen.