The intention was that challenges should be open to everyone and that everyone should be at even playing field so even rookies have a chance of getting to the top10 lists. But this might have backfired a bit since not having SSH greatly reduces keys dropped and the score loss is huge - dailies used to give between 30 and 40 million score, and now we have the #1 player in easy daily with whole 3 million score, getting whole 10 extra keys (compare to how much they lose by not playing on SSH).
The lack of SSH makes challenges highly bad in terms of rewards when compared to any other SSH mission (provided the player can compete on SSH level, which is like a big portion of this forum if I recall correctly) and also makes them laughably easy for any such player. Players literally go unprepared for the hard daily because free 55k (which is honestly a bit low of a payoff since the risk is huge, or at least was while we could fly SSH).
My suggestion regarding the unprepared medal is to greatly increase the bonus per stage as it exponentially becomes harder to obtain the longer the wave is, and only 5k bonus for an entire stage of 10 waves of risking a smallest mistake causing the player to forfeit the entire mission (which is an instant loss in challenges) is a bit low if you ask me.
(How did I get to unprepared medal from the topic being keys dropping from pointless enemies?!)