Funnily enough, this scene was one of the things that the person who recommended the game to me did spoil for me. Complete with the ditto part and a possible way how to beat it (which I'm proud of not having used so far).
I just thought "dude I wanna try and beat that now".
Arceus is a funny battle, because at first you'll go "what the hell, how am I supposed to beat this?", but not only can you easily try the Focus Sash + Perish Song combo mentioned above, but if you give it some thought (and your Pokémon some training) then there's many ways to deal with it.
I accidentally defeated it during a test fight in my last run, oops.
Personally I gotta say I liked that the game made me wait until I could get more of my favourite Pokémon. It felt almost nostalgic to me to be using a Noctowl for the majority of the game because I couldn't get Staraptor so quickly.
The game tries to be careful not to throw overpowered 'mons at you early on (though it can't be avoided with the starters... looking at you here, Blaziken), and I guess I just can't be bothered about whether or not I get to use my usual favourites. (Though thankfully, the majority of mine are in the game. Really, the only faves I can't get yet are Skarmory and the legendary birds.)
I can easily see how it's frustrating when you want to enjoy the game and its storyline while being accompanied by the kind of team that you'd want to have, but if someone really absolutely refuses to play Reborn because it doesn't let them have what they want immediately, then it's... kinda just not the right game for them.
The normal Pokémon games don't always give you your faves early on, either.
Whether it's B&W rightfully withholding Deino from you 'til you reach Victory Road, or certain Pokémon being reserved for the post-game, you'll always have to wait for things a bit.
That said (since I'm pretty sure I'm only repeating what others already said, bleh...
Cyrus is my favourite canon character in Pokémon, and the Tanzan Mountain Base arc was my favourite scene in all of Reborn. To this day I hope there'll be post-game content or something that'll let me have that specific Abra. (Though for now I like to pretend it's the one you get in 7th street.)