In Horde and Escape cards are awarded after each 5 waves or checkpoint respectively. Often these rewards are not what people want and include cards that are useless due to current meta, or cards that are almost always useless, like score boost. Low scrap payouts and not being able to scrap cards beyond max also negatively impact the user experience. As an example, playing 50 waves of Elite Horde only to get a bunch of greens cards already at max and completely unscrapable is infuriating.
The system on paper looks superior to Gears 4, but one small change I believe will make the grind far less arduous and give players more utility in how they spend their rewards.
The proposed change is simple, instead of awarding cards at the end of a Hive or Horde match, instead award the same value of scrap that it would cost to upgrade that card. Greens would award 40 scrap, blues 100, purple 600 and legendary cards would award 2400 scrap.
This way players would be less frustrated with only getting awarded green tier scrap as they can put it towards desired upgrades or craftable items from the supply pool.