Skipness
You are correct here, especially the last bit. The damage to Prestwick was caused by the owners seeing aviation, as so many still do with blinkers to everything else, as bucket and spade flights and using their airport as a feeder to the London, and now the European, Hubs.
Nobody with any future vision at Prestwick would have allowed the building of the shops in the centre of the runway line. To them 03/21 was sufficient to deal with any gale force cross winds and it probably was for what they saw as their mission.
Today, aircraft have changed dramatically with massive ranges and load/cargo/fuel capacities. Most companies look for long gentle take off runs to get these loads into the air without going to maximum thrusts on their engines. An extended 03/21 would give Prestwick this desirable capability, they could always move the shops if they had to.
Getting back to the prevailing winds there is some information and a compass rose on this Met Office site that shows that the cross runway was pretty much spot-on. The wind information is down at the bottom of the page. There is a compass rose for Tiree as well that you have to avoid.
https://www.metoffice.gov.uk/climate...al-climates/ws