Assuming you mean latency, Apple's unified memory isn't lower latency than other soldered or socketed solutions e.g. M1 Max with 111ns latency on cache miss vs 13900k with 93ns latency. Certainly not L3 level latency. Zero copy between CPU/GPU is great but not unique to unified memory or soldered ram.
As far as bandwidth goes, you would only need one or two LPCAMM2 modules to match or exceed the bandwidth of non-Max M series chips. Accommodating Max chips in a macbook with LPCAMM2 would definitely be a difficult packaging problem.
They have engineering difference. Depends on who you ask, it may or may not worth it