I dont mean this sarcastically or anything, I think this event has been one of niantic's best (if not the best) ideas.
What was the common complaint about CDs? There were so narrow in time window, it was easy to get screwed out of getting the moves. Solution, have it be the whole weekend where they are spawing in the wild everywhere and can get the moves.
The second biggest was what becomes of good iv version of these pokemon when their best move was event locked and their other moves cant even compete (examples like the starters and metagross, not tyranitar and dragonite as their other sets are different effectiveness on tyranitar and outrage > DM fr dragonite ). Solution, don't fret, these moves can come back, niantic isnt going to completely lock them away. I knew someone who after beldum day, traded all his for distance mirrors, got 2 lucky perfects (evolved one when an event happened hoping a mewtwo-SB like glitch happened, it didnt, and the second was evolved today for MM as he hoped it came back, and it did.)
And its not like players who have armies of these pokemon already dont benefit from this even if they have these pokemon en mass already. I and most of my community (and likely everyone else) is taking this weekend to collect massive amount of candy for these pokemon to power up. As mass evolving pokemon like beldum and starters depletes reserves very rapidly, getting a team of 6 eats away at ~740 candy. Without the need to mass evolve a bunch or frantically check iv's at the last second, we can spend a lot more time catching and building up candy, as well as trading, to get out good ones into the condition needed to be raid/gym worthy. After evolving 10 metagross, and 6 tyrantiar on their respective days, I didnt have anything to power them up and just remembered thinking how much of a slog it was going to be to power them up with all the candy I needed. This completely removed any bits of buyers remorse and got me and my friends able to use some of our favorites that much faster.
Hopefully niantic will continue these community days next year. If do, I wonder what we'll see next.