Taking good architectural photos is more than just slapping on a few filters, hoping for the best. You have to take into consideration a few different aspects to make the shot work. You have to consider the time of the shot taken, the direction of the source of light and the quality of ambient lighting you are getting. Usually, its more of when you shoot the building instead of what you put in front of the lens or what you do after you shoot the photo.
From the 1st photo, its obvious that the sun is shining from the side of the building and you were photographing the facade which does not get much light. In this instance, even if you able to extract details from the shadowed, the photo will appear flat and bland. Having an ND grad filter will prevent the sky from being overexposed but it will not improve the quality of light falling on the building.
Judging from the sun position, you were shooting around noon time? That's usually not a good time of the day as the sunlight is strong, harsh and very unforgiving. Depending on the orientation of the building, the best timing is usually 7:30 to 10:00 in the morning or 5:00 to 6:30 in the evening.