5G base stations in urban areas will be much smaller and won’t necessarily need masts as such. They likely will be on lamp-posts and the sides of buildings etc, rather than just on conventional masts and building roofs.
It’s not that 5G needs more base stations, but rather it can take advantage of more base stations to give more people fast mobile broadband simultaneously in the same place.
Also of course the radio signal (non-ionising radiation) strength from these small base stations will be much lower than with more widely spaced conventional base stations for 4G, 3G or GSM.
Also the mobile handset power will be lower with smaller closer base stations, which will also help battery life.
Fair enough! I was unaware of possible growth without PP - mind you, even requiring PP doesn’t prevent ugliness unless the local authority - and appeals process including secretary of state - specify criteria for appearance etc. ( I recall on holiday somewhere in Italy spotting mobile phone masts cleverly disguised as tree trunks (IIRC), so it can be done if the authorities require it.
It can be done for simple mast installations but there is a lot more electronics in the modern mast installations and antennas for multiple bands, so disguising them as artificial trees is not necessarily easy. If the local authority insisted on disguised masts, that would almost certainly double the number of masts needed and the cost of doing that might mean it would make more sense to the operator to leave the mobile coverage patchy there and invest in places where local policies mean the customers there benefit from better coverage instead.