How does Apple "ignore" MT performance? Yes the Max could have more CPU cores, but it would come at the cost of a weaker GPU or a larger more expensive chip. They're responding to what their customers demand.
Anyway, not having a Threadripper / EpyC / Xeon type chip that's all CPU without "wasting" space on GPU, NPU, display controllers and so forth is not increasing their ST. It isn't as if their P cores are too large to make a chip like that if they wanted, and their peak 1T power is less than AMD/Intel so they certainly have the power budget.
Not sure what you even mean with #2. Both AMD and Intel use chiplets, and have some designs where they closely couple LPDDR5X. How are those different than what Apple is doing. And yes Apple is using the best node they have access to. Intel was right alongside them with N3B, I didn't see them competing on ST though. AMD has deliberately chosen hang back on nodes, it isn't Apple's fault they've been cheap in the past. They're on board with N2 though so you won't have that excuse for much longer, though I'm sure you'll find another one!