Sorry, why is the arrowhead a "death trap"? One thing we do know is that manoeuvrability has a major impact on survivability. The extra mass of a larger half-saucer cruiser will improve survivability as well, and it's fair to note that, but let's not be unfair here.
Also on a different note, after re-reading the paragraph about the arrowhead design, it seems like the vertical nacelles are actually about offsetting an underslung deflector, rather than offering a second torpedo launcher. So it seems like the underslung deflector reduces our cruise speed at warp - depending on by how much, we may or may not care about the vertical nacelles.