Agreeing that MCM is better at all for AMD (performance wise), that it's not just to save wafers in 5nm as half of the chip is produced on 6nm basically, I would say that they still didn't use the possibility to produce a simply bigger chip - especially if you consider that with MCM it's easier possible than with monolithic.
That being said, latency is about 10% worse than with a monolithic RDNA 3, in this case 7600:
https://chipsandcheese.com/2023/06/14/latency-testing-is-hard-rdna-3-power-saving/
So, I don't see a upside in MCM aside from, again, saving wafers, and that is only so needed for AMD because they share it with their CPUs - something which would not be the case if Radeon would still be ATI.
Nvidia will go for CHIPLET as soon as it makes SENSE for them, as in, better performance or efficiency. Both things which AMD did not achieve this time.