Many companies have policies, especially when visiting China, to send in users with blank devices and wipe the devices on return.

The big 4 consulting firms aren't single entities. Each country has its own independent branch that shares a global brand, set if principles and objectives.

The Irish branch has to comply with EU and Irish law. Think GDPR and various other laws relating to keeping financial data secure. Plus they would also have very strict contracts with their bigger clients guaranteeing the security and privacy of their super sensitive commercial data.

You would be unwise to assume that the data retrieved through a customs search of your laptop or phone wouldn't end up in your rivals possession.

Because otherwise any information on the laptop would have to be considered compromised.