You have heard wrong - it's amusing that you're so confident in its failure despite having the wrong information.
There are two phases in the 5G NR standard. The first phase relies on some elements of the LTE control plane to coordinate data services. These data services use new numerologies for their OFDM modulation, vastly more flexible resource block, allocation, improved error control coding, lower maximum latency, better channel allocation, and standardized MIMO support - all of which will improve reliability and throughput, especially in crowded channel conditions.
Phase 2 formally introduces millimeter wave signaling - this is what does primarily propagates through line of sight (LOS) channels. Clever beam forming and beamsteering can alleviate this to an extent but these cells are intended for dense urban environments or interiors of large buildings. These will supplement the lower frequency bands when available but 5G NR devices will still use the lowband when mmWave is unavailable. Phase 2 also switches over to an entirely 5G NR backed control plane (Standalone, or 5G NR SA) which has its own reliability and throughput improvements though these will all happen in the lowband since mmWave isn't suited for these tasks.