Hmm, you are right. I forget the Custodian has a tracker in it too.
The only reason I can see that makes the Messenger useful is to stick it in a squadron of other escorts, Castellans or Defenders, and keep it at the back. But yes, knowing that it cannot benefit a Custodian, this brings it's usefulness down a ways.
Personally, at bare minimum, I think its WBs should be brought out to 45cm. The point cost is something that could use some reworking also.