I think it's really annoying in combat mode that you can't see the other sub as a waypoint.
The map is huge and the chances that you will miss the other sub entirely.
I have multiple solutions for this:

-The waypoints update every 2 minutes only
-You can tell the general direction of the enemy (left, right, up, down)
-You can always se the location of the enemy but the nav terminal has an option to mask location for a few minutes every 10 minutes.

But that would defeat the purpose of stealth, There would be no reason to try and blend in with the rock formations. The maps themselves aren't exactly huge, and the only way you'd miss a sub is if you drove under it or over it. Not to mention if the enemy sub goes too far down they will compromise themselves. Within range of another sub you can also hear the pings of a separate sonar if their system is on as well.