Risking the future of your business for a 20% customer sounds like a tricky proposition, and moves like this have real risk for TSMC.
It's hard to predict the future; and the whole point of a foundry and why TSMC has been so successful is because they refused to play that game. They kept their options open and flexible rather than betting on a few key chips, and they've repeatedly pointed out how the very diversity of their customers has meant they always have some customer willing to be a guinea pig for some new tech.
Losing diversity is a cost; it undermines their very business model. From a business perspective you'd hope they really made apple pay through the nose for that cost, and not just acquiesce because they're a significant customer.
I'd say it's at least plausible that TSMC miscalculated here, and didn't think AMD and Qualcomm (and perhaps others) would dare.
To be clear: they might still get lucky (and AMD/Qualcomm unlucky) - it's not exactly news that new process nodes sometimes fail or are delayed, and if Samsung turns out not to be able to deliver, they'll be able to reacquire that diversity with little trouble, surely. And if they can replace AMD/Qualcomm with other leading edge customers they might not even really be losing much of that diversity they value so highly.
Apple is also the biggest customer for Samsung, outside of Samsung themselves. And they have preferential contracts with Samsung, too. Enough that Apple has required the Samsung chip manufacturing subsidiary to operate with Chinese Walls between them and the other Samsung businesses, and sometimes Apple gets preferential treatment over those other Samsung businesses.
So, this is a frying pan versus fire situation. I don’t think AMD and Qualcomm are doing themselves any favors here.
Do you have any link or data to back that up? Obviously, Samsung isn't entirely open about who's paying it how much...
Another large customer (that will be jumping ship to TSMC) is Nvidia, and clearly Samsung isn't supplying any of apples core SOC's anymore, so what is Samsung providing to apple that's valuable enough to make apple it's largest customer?
Apple is not known for overpaying. Apple is however a significant volume customer and volume customers usually enjoy a huge discount that smaller customers don't get. So in addition to preferential allotment, Apple is probably paying less for the same node.
Apple may not overpay, but if they're willing to pre-pay multiple billions of dollars that's a huge incentive for a company like TSMC, who gain the ability to instantly (well, "instantly") launch capital projects, rather than having to wait for three years of revenue to roll in first.
For all we know, TSMC is taking all that 3nm Apple money and putting it into producing new 3nm fab lines, which would honestly be better for everyone in the long term (except Intel, I suppose).
Sure, Apple's prepay financial arrangement might have some outsized influence in smaller, riskier, or declining businesses, such as GTAT or JDI, but there is nothing special about pre-pay, especially in this market and this particular industry. Top fabless makers from Qualcomm, to nVidia, to AMD, to TSMC are flushed with money and are desperately competing for capacity. In fact, TSMC recently disclosed that they received over $3.8B in such prepay, or "temporary receipt" from various customers for their future nodes [1].
Further, Samsung and TSMC routinely spend many more billions on capex every year. Both companies not only have many billions stashed away, but also have the means to finance them without relying on Apple. For instance, Samsung's capex in 2020 was nearly $30B; TSMC ~$25B, vs Apple's $7B.
Sure, Apple is a big consumer of the latest nodes, but the process nodes will advance with or without Apple or Apple's money.
