I'm against map updates, even in SH5. Stadimeter shows distance little of, but range estimations for estimating speed are equally off, so you can get correct speed. Atleast I think...
What I do is I'll try to reach about one kilometer distance (at this distance stadimeter is accurate enough) at good angle to fire. On the way to good firing position, I take sightings of the target, mark them on the map (Also mark my own position to see my relative speed at the enemy). Then I draw line through these marks and get reasonably accurate course for enemy ship. Not every shot is a success, but enough to give a feeling that you can do your job! Here is screenshot of one of my approaches. I get the AOB from the estimated enemy course. I fired 2 torpedoes with correct data in tdc, and then third a little later (wich was a mistake, because the data was not valid anymore... it missed.)
But all I wan't to say is that even if stadimeter is not what it should, you can use it and play the game with map updates off.