There's a chance you can get engrams from the Strikes. There's also a chance you'll get nothing until the end reward screen. I've had several strikes where the only worthwhile rewards I got were from the end game screen, and I did stop to fight everything, as I used to be like you. However, since the patch where 24 Strikes give engrams, I've seen less and less engrams drop, not just in strikes, but in general. I went through several strikes getting nothing but a few greens, killing everything in sight. So yeah, now I might skip a few enemies here and there, because personally for me, odds are I won't get anything as the game has shown time and time again. Also, if someone does stop to kill everything, as long as I aggro them with my speeder, any blue drops will appear at the postmaster. I don't mean to sound bad with that, but it's true. The first day of the update I got a crap ton of blue engrams, but the drop rate of them seemed lower and lower as time went on. Edit: I found 5 purple engrams on the day before the cryptarch update, and have only found 1 since, on a level 12 story mission for the Queen. Second Edit: Also, unless those engrams are dropping Raid Armor, I have a fair amount of everything I really need at this point, and the odds of getting an engram that will contain the one Exotic I want are so astronomically low that why should I bother trying to find a random engram amongst the level 2's before the strike?