As they have not yet posted how ratings/rewards will work for season 2 I am assumed season 1 conditions. For season 1 your rewards were based on your highest rating achieved not the rating you held on the last day.
Now assuming that condition, if I have achieved my necessary rating there is no penalty and no risk to throwing away games in order to complete the daily/weekly.
Considering there's a top 3 reward, I wouldn't be surprised if they made it based on the last day's rating . I think that way's better honestly, as long as they release percentile marks for reward tiers instead of straight up Elo marks.