Antenna theory

This is true for radio planning of mobile-cellular networks where they use high gain > 15 dBd and sectorised antennas with horizontal opening angles of 90 and 65 degrees. These antennas have a relatively narrow vertical beamwidth that may result in a lack of coverage nearby the site.
Regular Omni-antennas as used with LoRaWAN does not suffer from those problems.
In practice, the antenna gain for LoRaWAN antennas is not a serious topic.