> GC burns far more CPU cycles
Far less for moving collectors. That's why they're used: to reduce the overhead of malloc/free based memory management. The whole point of moving collectors is that they can make the CPU cost of memory management arbitrarily low, even lower than stack allocation. In practice it's more complicated, but the principle stands.
The reason some programs "avoid the heap like the plague" is because their memory management is CPU-inefficient (as in the case of malloc/free allocators).
> Meanwhile I'm not sure where you got this idea about the value of CPU cycles relative to RAM
There is a fundamental relationship between CPU and RAM. As we learn in basic complexity theory, the power of what can be computed depends on how much memory an algorithm can use. On the flip side, using memory and managing memory requires CPU.
To get the most basic intuition, let's look at an extreme example. Consider a machine with 1 GB of free RAM and two programs that compute the same thing and consume 100% CPU for their duration. One uses 80MB of RAM and runs for 100s; the other uses 800MB of RAM and runs for 99s (perhaps thanks to a moving collector). Which is more efficient? It may seem that we need to compare the value of 1% CPU reduction vs a 10x increase in RAM consumption, but that's not necessary. The second program is more efficient. Why? Because when a program consumes 100% of the CPU, no other program can make use of any RAM, and so both programs effectively capture all 1GB, only the second program captures it for one second less.
This scales even to cases when the CPU consumption is less than 100% CPU, as the important thing to realise is that the two resources are coupled. The thing that needs to be optimised isn't CPU and RAM separately, but the RAM/CPU ratio. A program can be less efficient by using too little RAM if using more RAM can reduce its CPU consumption to get the right ratio (e.g. by using a moving collector) and vice versa.
Moving collectors as generally used are a huge waste of memory throughput, and this shows up consistently in the performance measurements. Moving data is very expensive! The whole point of ownership tracking in programming languages is so that large chunks of "owned" data can just stay put until freed, and only the owning handle (which is tiny) needs to move around. Most GC programming languages do a terrible job of supporting that pattern.
That's just not true. To give you a few pieces of the picture, moving collectors move little memory and/or do so rarely: In the young generation, few objects survive and so few are moved (the very few that survive longer are moved into the old gen); in the old generation, most objects survive, but the allocation rate is so low that moving them is rare (although the memory management technique in the old gen doesn't matter as much precisely because the allocation rate is so low, so whether you want a moving algorithm or not in the old gen is less about speed and more about other concerns).
On top of that, the general principle of moving collectors (and why in theory they're cheaper than stack allocation) is that the cost of the overall work of moving memory is roughly constant for a specific workload, but its frequency can be made as low as you want by using more RAM.
The reason moving collectors are used in the first place is to reduce the high overhead of malloc/free allocators.