IMHO, it's better for Apple to be a foundary customer than to run an internal foundary.
As a customer, if TSMC falters, they can switch to Samsung or Intel (if Intel foundary materializes).
As a vertical foundary, it's very hard to switch if it falters. AMD managed to spin out their foundry which was becoming non-competitive and switch to TSMC, Intel has a lost decade because of the pipeline bubble caused when the Intel 10nm foundary arrived late and with poor yields.
Apple has a very hard time selling to business, and I think would not be able to credibly provide foundry services to others, so it only works if they can keep it on the leading edge.
As a customer, if TSMC falters, they can switch to Samsung or Intel (if Intel foundary materializes).
As a vertical foundary, it's very hard to switch if it falters. AMD managed to spin out their foundry which was becoming non-competitive and switch to TSMC, Intel has a lost decade because of the pipeline bubble caused when the Intel 10nm foundary arrived late and with poor yields.
Apple has a very hard time selling to business, and I think would not be able to credibly provide foundry services to others, so it only works if they can keep it on the leading edge.