In the real world I don't have an array with over 2^30 elements 99.75% of the time. If I did need to process an array with over 2^30 elements, I'd have dozens of reasons to worry that standard techniques might start failing, and would therefore carefully consider and test everything to a much higher degree. I'd want a safety margin of at least 10x, which means I'm designing for 2^33+ and already know I need to avoid int32 everywhere I can. The type signature of a binary sort returning int32 in such a case should already be triggering alarm bells.
This is a bit like arguing that every building humans have built is flawed because it wouldn't withstand a significant meteor strike. That's not how we do it. We consider maximum likely use cases and then build in safety margins of at least 10^2, sometimes up to 10^6. If you think there's a possibility you're dealing with hundreds of millions of elements, you stop using int32 entirely. You don't wait for 100 million to turn into 4 billion and crash.
This is a bit like arguing that every building humans have built is flawed because it wouldn't withstand a significant meteor strike. That's not how we do it. We consider maximum likely use cases and then build in safety margins of at least 10^2, sometimes up to 10^6. If you think there's a possibility you're dealing with hundreds of millions of elements, you stop using int32 entirely. You don't wait for 100 million to turn into 4 billion and crash.