I do see what you're saying. However for lower level players this does help quite a bit. It takes a good deal of time getting to Navigation..Players that are taught to  level each discovery to lv20 it will take them longer. Also  another thing to consider is odds are you're stuck dealing with the dragon sketches. Heat 2 isn't that great in comparison reward units are actually worse.(buccs and skirms) That's a first. Anyways though if players are in a BH that teaches them to play the lh properly getting a good number of unit rewards will benefit them in the long run. Getting 500 points for the first prize isn't that hard. Also these rewards can help players to push on to the last 3 heats.  

On a final note though, fleets aren't built they're won