The P-8A can fly low level with no issues at all and can be fitted with a MAD boom; one customer has already chosen this option.
Try to think of the P-8A as an MMA than can also conduct its ops from high level. The high level capabilities are a bonus but when you are chucking out cheap stores, working in the visual domain or just reducing the RF horizon you will find the P-8A working at low level just like every other MPA.
The urban myths of the P-8A being incapable of traditional maritime flight profiles are just that - urban myths. It has plenty weight growth potential too.