I only read the original post, so sorry if I missed something you already answered or something that was discussed already.
From what I read, it sounds like you need to take a step back from the Animal Crossing community. Maybe you feel anxiety from not having the same experience or outcome as other people?
Aya Kyogoku said that this game was made to be played at least for one year and I was like "gosh, if she said this, is because New Leaf wasn't expected to last this long, but I played it for more than 4 years, so how much will last New Horizons for me?".
I think this more means that you can expect new content throughout all 365 days, but not new stuff everytime's there's cherry blossoms f.e.
Are you a time traveler? Because if you're not the content wasn't available more quickly in previous games, and if you are it's easy to burn out due to doing too much at once.
Before easter day, you received a letter from Zipper T. Bunny and attached to the letter, there's a ticket. You bring that ticket to Porter (who will wait for you with an hot air balloon in the plaza) and he will bring you to the Easter Island. This is a special island you can only visit on easter day and it's full of themed houses and decorations.
No Animal Crossing would ever be this complex though, especially not for a day. Events were always grinds for seasonal items. Of course Nintendo can do a lot more with the island mechanic, but you need to realize that they have plans they want to pace. We got a May island.
You could go to Tortimer island and play lots of funny minigames or collect fish,bugs or dive together to collect fish creatures. Now all of this stuff is disappeared and the only thing you can do is run around the isle collecting fruit, fishes or bugs.
Tortimer's Island missing is a shame, but I think the japanese commercials made it seem like with 8 players on the island you're supposed to create your own fun with it and roleplay a little bit. Also, we don't know what's still to come. We're evidently going to get more than expected.
while you are playing with somebody, you need to pray for connection to don't stop,
Pretty sure New Leaf didn't do it differently, but you need to realize the changes that needed to be made for 8 player online multiplayer. Imagine if all 8 players wanted to save at once, especially with how long the loading times already are with the new engine and all that.
I'll not mention the fact that this game was designed to force you to play with other players (for example, you can't get different fruits from your native and sister one, if you don't get them from other players).
You couldn't get more than 3 flowers until Nintendo decided to give you your missing flowers through Leif. What are you in a rush for anyway? We don't know what festivities we're going to get through the seasons, we might as well have a "new" NPC selling fruit in the summer.
New Leaf had 14 different buildings
Yes and most of them were unlocked a month after the last one opened. Nintendo has limitations (no town street) and opportunities (islands). We don't know what's going to happen in the game, we just don't. Even if we can only shop furniture and clothing, NPC can still come and offer their services in a different way. Don't stress yourself out over possibilities.
turns out that they are just a bunch of pre-existing island and after you have all plots full in your island, you will not see new villagers on mystery isles.
Not sure how you were expecting Nintendo to handle random islands? They can't design hundreds of islands, and leaving it up to a random generator would just be annoying most of the time. I agree though that there could be more to do, we need more diverse mystery islands.
Also, would you like to see random villagers if you didn't have the ability to invite them onto your island? I don't think so.
Villagers always repeats the same things and if you get 2 villagers of the same personality it even gets worst
A lot of the dialogue was added for a bunch of furniture item and clothes, so maybe they're lacking some for regular dialogue but at the same time they also locked them with friendship levels. For the personalities, they can't exactly add original dialogue for hundreds of villagers, but we could definitely do with some sub-personalities so that the dialogue can be divided to both of them.
As for the mean thing, try doing mean things to the villagers. I opened a present and the villagers really weren't too kind about it.
Designs and Pro-Designs are two different categories with their own storage. And you need Nintendo Online to access other people's designs, something that is available through a free trial that was just resetted for people who already used it. But you don't even need them.
Some players were also kind enough to share their designs not as a code but as they were drawing them, so you can just copy their colors.
And let's not talk about creating repeated items.
You can just button smash though, the cursor will always go back to the last item you crafted. When I crafted 30 bait it wasn't too bad.
Crafting is an experimental part of the game, but you're not forced to create tens or hundreds of items at once. Take your time with it.
After one month, my island is almost complete.
Luckily this game isn't called Island Designer, huh?
I'm at 360+ hours of gameplay
That's at least 8 hours a day, this is definitely a burnout.
(you can do this in half an hour)
You don't need to play the game for more than half an hour a day if you don't want to.
I think that the biggest problem for me is that the game is incomplete for now, compared to New Leaf.
Are you sure you felt satisfied after 6 weeks of playing New Leaf? Or are you just fond of your time playing back then?
Not sure why I felt the need to reply to statements, but the bottom line is that your perspective is very delusional at the moment, as you like to put it. You're making things worse in your own mind, and there's nothing wrong with that. You need a break, so take it. You should have fun playing Animal Crossing, maybe taking a step back will help you with your frustrations. We'll be here for you if you're looking for fun.
The game definitely has a lot of problems and nobody is having complete faith in Nintendo to do everything right, but you just gotta take the good with the bad. New Horizons looks amazing, we have so many new options and we still have 9 months of new seasonal events to go!
We are all different so it's normal that we can't all have the same feeling about the game 
