Actually, you didn't. You claimed broadcasters weren't using all of their bandwidth, but they are. Even if they have no subchannels, they can still be using the entire 19.39Mbps bandwidth.
Again, the repack does not change how MUCH bandwidth is used, it simply changes WHERE it is used. So channel ABCD, currently on channel 41 is getting repacked to channel 23. They still get the 6Mhz wide channel they had on 41. It doesn't matter if they're using it for a single channel or 6 channels. ATSC1 still limits them to 19.39Mbps.
ATSC3.0 implementation could change how many channels are out there. Let's say you have channel ABCD which has CBS, MeTV, AntennaTV and LaffTV. In the same market is channel ZYXW. They have NBC, MyTv, and CW. One possible to accomplish the transition is ABCD puts up an ATSC3.0 transmitter. Because of 3.0 allowing more data, they agree to broadcast ABCD's CBS and MeTV AND ZYXW's NBC and MyTV.
In exchange, ZYXW agrees to broadcast NBC, CBS, and (possibly) CW using their ATSC1.0 transmitter. So AntennaTV, LaffTV, and MyTV all go away until both stations fully launch ATSC3.0. (note: I'm making up the situation, it's possible one or two of these survive).
The bottom line is the repack has NOTHING to do with bandwidth usage (other than any channels above 37 will need to be vacated).