Yeah, the four PCR tests (one 3 days before departure, one at the airport, and then two more during the stay) seems excessive and pointless. They are also a bit expensive (I was quoted 4k or 5k in Bangkok).

Edit: the ShaThailand FAQ seems to imply that you can use the rapid test, which is cheaper:

"RT-PCR test:
– Every hospital in Phuket can provide an RT-PCR test;
– The cost of an RT-PCR covid test ranges from 2,500-4,000 Baht per person.

Rapid test:
– You can get a rapid test from hospitals, clinics, and private labs in Phuket;
– The cost of a rapid test ranges from 450-1,000 Baht per person. COVID-19 testing is at the travellers’ own expense."