1) That the final 22 quests of a 22 day event are unlocked for one a day has been a part of the events for a while, I think predating the introduction of Leagues by a number of events.
2) Everyone experiences the same quest locking. You are being held up on finishing all the quests the same way every other player is. Consider this... a player who pushes through quests faster, whether with more Manus/Factories, or more Spells, or more Time Boosts, or whatever, will hit the locked quests sooner and slowed down longer.
3) Quest locking towards the end... was that really holding you up all that much? In the final week, each quest only gave 70 or so Sky Essence. I had waited until two days from the end and had collected around 5,500 Sky Essence without the final two Quests. 145 additional Sky Essence at that point would have only added about 2.5% more Sky Essence (which I did eventually get). How much are these final quests really holding you back? Would that additional 2.5%, 4%, 5% really have made that much more of a difference?
4) Perfectly fine to want to see how far you can go. Having said that, you should probably consider the ramifications of pre-setting an arbitrary goal, whether a target Percent/League, specific Feather amount, or even a Feather amount based on expected currency-to-Feather ratio. Again, for personal goals you have a lot less control on shaping any particular outcome, as the RNG plays a big factor outside your control, and for competitive goals, almost assuredly there will be some players who have better RNG outcomes than you do, and those willing to pay can top any non-payer if they wish.
5) Finally, I think everyone needs to take a giant chill-pill over the "Falling Backwards" feeling over Percentile performance and Leagues and reassess why they are feeling the way they are. The game's not over until the game's over. Despite the fact that we all start at the same time, Leagues are not a first-to-the-finish marathon, but rather a best-performance-takes-the-medal competition, and not everyone finishes at the same time. Baseball, Hockey, Football (American or European), Tennis; winners aren't declared before the time runs out because last-minute upsets happen. Skiing, weightlifting, gymnastics, pole vaulting; the final contestant could still end up besting the field , Elections aren't called until all the votes are counted. You are celebrating too early if you are looking at your League standing any time before the close of the Event.