Actually, I'm a little curious as to whether this was all out overkill based on some earlier rumors. Either way what they've done here looks great.
With the rumors of AMD's Big Navi GPU, the model in which seems to be what the PS5 GPU is based off of, leaks show it could be capable of 2.5GHz max boost. If SNY was originally shooting for this, or as close as possible, they almost certainly would've based the cooling system off of that, considering it would be the worst case scenario in terms of thermals. Maybe even the CPU was originally planned to have been clocked somewhat higher as well, since XBSX has higher CPU clocks.
With the CPU and GPU being clocked at where they are now, it could be the case that SNY wasn't quite able to hit their assumed peak GPU clock, and therefore also were ok with a slightly lesser CPU clock as well to go along with it. Not much point in having excess CPU or GPU clocks for little reason in a balanced system. This would also help with APU chip yields and costs.
If the close to final silicon wasn't quite able to produce the upper limit of their goals, SNY should've already had the cooling system finalized by then. This would mean since the APU clocks ended up slightly lower than anticipated, the cooling system would be a little bit overkill, and likely too late to change it. Instead of having to cool around 11.5TF of GPU performance, it would only have to cool 10.3TF.
This also makes me wonder about the PS5 testing rumors of it running hot. If the reason for the liquid metal was due to having to potentially cool the GPU, and possibly CPU, at higher clocks than now advertised, since they ended up below those goals by a little bit, perhaps they decided to try and test with a cheaper thermal paste as well. They could've tried a higher end carbon based paste, which would've saved them some money, if it would've performed sufficiently.
Then we heard afterwards (can't remember if it was rumor or legit), that SNY had chosen to go with a higher end, more costly thermal solution. I wonder if they tried carbon paste, found it didn't quite keep the system cool and quiet enough, and decided to stick with the liquid metal anyway. Play it safe, and be better safe than sorry later on.
Did SNY have higher clock goals in mind initially, and would the PS5 had run near as cool and quiet in this same configuration if they had met those goals? This is just speculation. I don't have any particular reason to believe this is the case. The question based on the rumors and final outcome just came to mind.