Unless there is relay or other equipment colocated, which is common, the cell 'portion' of the antenna system or site is typically very low power. This is dependent on the density or distance between the site(s) in a particular area.
In addition the [mobile] antennas are directed down a few degrees towards the intended location of the users- i.e. on the ground.
There are some 'tower' guys around here. Maybe one will chime in to elaborate in more detail.
Yes, I enjoy asking them questions when they come to service or add another carrier as they did on one last year. 50 watts is all each 'antenna' up there is (the antenna's have front end and transmitter stages in them too if I understood them right...