how is that more valid than saying usize should coerce to [*]T because you can do ptr arithmetic with usize?
because that is literally what your bypass is;
ps - pm produces a usize, which you are then adding to pm.
ps - pm is certainly useful, if ps is a pointer to an element within pm, then ps - pm will give you its index.
pm + n is useful, it is literally just indexing, whether zig should have multiple ways to index is a different discussion.
This whole thing is just the result of [*]T not having bounds, which lets you access arbitrary memory.
This is not at all an argument for allowing *T -> [*]T coercion.