If you want the same memory bandwidth and latency in your windows laptop, you would similarly need to have soldered LPDDR5 memory and pay the premium for it
You pay a premium for GDDR or HBM because they're actually faster. LPDDR5 isn't, Apple just used the equivalent of a larger number of memory channels to increase the memory bandwidth (x86 servers do the same thing) and then charges a premium for the ordinary memory chips because they can get away with it.
Moreover, there is an obvious way to solve this without soldering the fast memory to the system board -- you solder it to the CPU. This is not only lower latency (traces don't have to go through the system board at all) and lower cost (don't need extra pins between the CPU and the system board), it allows you to upgrade the memory by upgrading the CPU. And isn't incompatible with still having dedicated slots on the system board to add additional memory with less memory bandwidth. Which is typically what you want anyway because if you're going to solder something to the processor, you're better off to actually use HBM or GDDR (which is even faster), but then you don't want all of the system memory to be that because it costs more, many applications don't need it and cache hierarchies are a thing for a reason.
Moreover, there is an obvious way to solve this without soldering the fast memory to the system board -- you solder it to the CPU. This is not only lower latency (traces don't have to go through the system board at all) and lower cost (don't need extra pins between the CPU and the system board), it allows you to upgrade the memory by upgrading the CPU. And isn't incompatible with still having dedicated slots on the system board to add additional memory with less memory bandwidth. Which is typically what you want anyway because if you're going to solder something to the processor, you're better off to actually use HBM or GDDR (which is even faster), but then you don't want all of the system memory to be that because it costs more, many applications don't need it and cache hierarchies are a thing for a reason.