One major downside I'm seeing of this new form of the event is that at times there's effectively little or nothing to do, sometimes for long periods of time.
When there was a set quest list you could plan things in advance, and so could always be working on multiple things in advance, so most of the time there was lots to do, putting in or taking out level 1 buildings, putting on productions, organising things, etc. The exception is when the very long scout quests came up, which is a problem no matter what form the event takes, but it's not like the entire event consisted of nothing but these. Most of the time there'd still be lots to do.
When events switched to the random endless series of quests you could still plan things in advance, such as having a variety of productions running or ready for pickup in level 1 workshops, tier1 manufactories, MA, crafting, putting a scout on, etc, so there was still lots to do that you could do in preparing for the different types of quests that might come up.
With this new event form, where most quests need large workshops or manufactories, almost everyone is limited to only a very small number of these due to the space, population, and construction time required, so there is much less that can be done in advance. You're pretty much limited to working on only one quest at once. It doesn't matter that we get more event currency from completing the quests to compensate for less quests being completed. The issue is that there's nothing to do for the event for long periods, and this is a very frequent, so it's boring. You just collect the production for the current quest, put the next one on, then wait around til it's complete. That might be the next day, so everything you've done for the event that day takes less than a minute. That's simply not fun. There might as well not be an event.
Of these three forms, I think what worked best was the endless quests without the high level requirement for production buildings. If the endless quest format meant some people won too many prizes then you should cap the amount of prizes that can be won, or make it much more difficult after a certain amount have been won. Doing this indirectly by preventing people from engaging in the event to any significant degree is simply silly, and just creates frustration and prevents people from having fun. It's one thing to come up against the occasion quest that takes an unreasonable length of time to complete, it's another for this to be literally every single quest.