Tangent subthread on a "how to fix the trashcan" (thermal management)
Copper will do no such thing. Magical heatpipes and water coolers aren't either given the same physical volume and fan airflow constraints.
This is the start to a good observation.
To distill it to core essentials, there's two basic things to keep in mind, namely (1) heat spreaders and (2) heat rejection.
For (1), there are heat spreader (and heat mover) technologies that are better than what Apple used for the core of the Trash Can, which includes simple stuff like using copper for better Thermal conductivity, as well as more exotic solutions, such as liquid cooling, heat pipes, or even TPG (Thermal Pyrolytic Graphite). However, all these do is to move the heat from its (increasingly high density) source to some other location, where it is more readily rejected overboard, which is step (2).
For heat rejection (step 2), the only venue that PCs have is effectively into the atmosphere (air), so a source-to-air heat exchanger has to exist in some form, and because air has a low heat capacity, as the thermal load goes up, it means that you need to move more & more air over/through your heat exchanger.
Even for a fanless laptop, which tries to use natural convection on a slab exterior surface, that's still a source-to-air heat exchanger.
Again, while there are some interesting heat exchanger technologies ($$) which can offer higher average efficiency values, these are not also without their design trade-offs. For example, metallized open-cell foam is more efficient than traditional "fin" designs, so you can have a smaller heat exchanger ... but the same design attributes which let you shrink the heat exchanger makes it more vulnerable to clogging, so you end up with more stringent air filtration requirements to pay for...ie, a bigger air filter and bigger fan (and bigger power to run it).
The resulting trade space may or may not be worth it, depending on how far you have to move the waste heat before you can finally get it overboard, along with what your space budget limitations are for each stage.
FWIW, I was closing this by saying "...but of course what always screws over the ME who's been given the thermal management design task is a project manager who insists that Jony Ive's aesthetic wishes can't be compromised...", but Apple's engineering group's problems run much deeper than merely thermal management: these are largely been very much self-created problems and span multiple engineering disciplines, such as has been recently illustrated in a wireless mouse that can't be used while its charging, and the multiple tries to fix the MBP keyboard...
...and it looks like that within Apple Leadership, this is the responsibility of Dan Riccio.