With your cap method you have reduced the volume of water available to just what can be delivered by the single cold water pipe. Before you have the volume of the hot + the cold. You might not have as strong of flow. You could test this by seeing if the cold water alone will provide enough pressure for you now.

With your cap method you have reduced the volume of water available to just what can be delivered by the single cold water pipe. With current hot/cold piping you have the volume of the hot + the cold pipe - obviously greater than the cold alone. With just the cold will not as strong of flow (volume or pressure). To determine if the cold flow alone will be adequate, just run each fixture with the cold alone on high and see if you are satisfied with the flow. If you are satisfied, the cap method should be fine.