Silvy already pointed out what the problem with Daring Don't and the world was but I'll reiterate: Twilight is supposedly a huge a fan of the series, going so far as to know where and when Yearling was born and so on, and is able to get her address just like that. How hasn't she at any point heard of any of these troubles? Why hasn't anypony else? Why haven't the villains searched for "Yearling's" address and ambushed her there earlier? Yes, you are right that most ponies don't remember the six as the Bearers of the Elements, that much is true. Most of the time it isn't really relevant, anyways but in the episodes it is, ponies remember it. This is an episode where it would have been relevant for ponies to know Daring Do existed but nopony knew it. Though to be fair, I'm not a huge fan of them being the heroes of Equestria in one episode and noponies in the eyes of others in the next, either. But as said, most of the time it isn't relevant but when it is, I dont' like it, either. That's just such an old thing that I don't bother bringing it up anymore or I would have to mention it with every episode. The new (and worse) version of that is Twilight's princesshood which is simply forgotten about even though she has two big reminders with her all the time (see: Rarity Takes Manehattan).
>in a world of magical monsters and colorful ponies, anything can happen
Only on the Hub!
Erm, I mean… Things that break from the norm and that introduce competely new things to the world need to be explained. As an example, wouldn't you find it reasonable that there is a griffon settlement just next to Ponyville? Probably not, because if there was one we would have seen way more griffons in the show and them just suddenly appearing would be jarring. In a vacuum such a thing would be just okay, since in a world like this there isn't really anything saying there couldn't be griffons living next to ponies. But in the context of the series as a whole it doesn't work as a place next to Ponyville because it would have made itself known earlier.
As you said, it is very likely a difference in approach. You just sit back and watch ponies and take whatever they give you. I sit back and expect a somewhat cohesive world that has a history and which stays the same throughout the episodes. If in one episode we are shown Scootaloo's parents (or were told she was an orphan. Either way) I would find it just natural because it doesn't go against anything established previously and isn't that big a deal, even if it could be weird it was never brought up before, But if it wasn't relevant, fine. If Rarity or Applejack was told to have another sister who they love as much as they do the ones we have seen and their appearance was treated as if they had always been there, it would be jarring. …Just like Mare-Do-Well and suicide road or the loner Twilight who never had a friend or knew the value of friendship before coming to Ponyville actually having a BBBFF and a foalsitter who she considered a friend and with whom she had fun.
>world started with no alicorns
Also, if ponies could ascend, shouldn't there have been some fairytales about other ponies ascending as well? Cadence might or might not have ascended, the show doesn't say (I don't consider the books canon unless confirmed in-show) but the biggest thing with her appearance, at least for me, was another alicorn just suddenly appearing out of nowhere and it never being addressed at all. It still hasn't been, and for a show that from the very beginning promoted two regal sisters who ruled the day and night having a third one come out of nowhere is jarring. Had it been explained I would have been way more than okay with it. Cadence is
such a cute pony, even if her character can be a bit flat.
So, to answer your question, the thing that makes it weird is the lack of explanation and treating it as if it was nothing. Yes, yes, I know ACW had a lot on its plate as it was and having them explain alicorns would have made it even worse. Same with MMC. BUT, that is a big mistake in and of itself, and the main reason I don't like MMC isn't Twilight becoming an alicorn, but the way it was done and the episode just being the clusterfuck it was.
Ascension to alicornhood was treated as a reward of some kind for showing she represented all the elements of princesshood and having created new magic but all she did was fuck up Starswirl's spell, mindrape her friends and the whole world, make Fluttershy help RD and realize who she was, and then just let her friends do the work. …and then suddenly just finish the spell with an epiphany out of nowhere, related to nothing in particular and BAM, wings. Making new magic? Starswirl created tons. Using the magic of friendship? Not relevant in this episode, her friends fixed themselves pretty much on their own and the only spell she cast made her go poof. So why is it Twilight that ascends, are her friends less worthy for whatever reason even though they have done just as much as Twilight, if not even more.
The episode had way too little time to do the things it wanted. It wanted to be a musical, it wanted to have a storyline about swapping cutie marks which by the way seems really, really wrong to me, considering cutie marks had been established as being somewhat magic proof in Call of the Cutie, not to mention the whole "mindraping the universe" business
and it wanted to add in Twilight's ascension to alicornhood to the mix. Ignoring the problems with swapping cutie marks, any one of those could have been at least a single episode, if not a two-parter or longer in the case of alicornication. Them not having enough time made the whole episode seem like a mess with Twilight's huge revelation and reward just seemingly tacked in there and her being rewarded for nothing in particular. They had achieved bigger things before already, so why was this so notable?
To me it seems clear they either had no idea what they were doing, or, as anon said before, were just quickly trying to wrap things up in case the show went away and it shows. I'll be frank, I would have no problems with Twilight being the only one of the six who ascends IF it was explained and the episode gives a good reason for it. Had they simply gone with "Twilight, your destiny is to become a princess!" I would have been happier than her being "rewarded" for doing nothing at all. The execution was all kinds of flawed, and these questions never having been addressed realy grinds my gears, and is the reason I don't like MMC at all. …and of course, as Silvy said, "Twilight and sidekicks" was and is a big problem, too. Especially in a show that seemed to promote friendship and everypony being equal and needed. Twilight ascending is something I sometimes thought could happen at the very end of the show, since Twilight has been somewhat of a main character, and her learning about magic, friendship and life has been a theme. Her growing into a position of leadership could have been interesting to watch, but not like this, and not yet.