4G used clever ideas to get much better practical spectrum efficiency than people thought was possible... At the cost of very expensive infrastructure. The biggest selling point to carriers was standalone 5G networks that were cheaper to build but paradoxically carriers are prone to frame 5G as a feature customers pay more for.

The area where wireless networks fall short is coverage. Obviously many homes and businesses are difficult to cover with wireless technology. Also many "IoT" and public service situations need wide coverage, and a network that works in 92% of places is "close but not cigar." There are few obvious answers rather than "lots of fiber and very cheap small cells" and "satellite technology" but it's what it takes to address wireless use cases that currently aren't addressed.