You can individualize the character's looks and how you interpret the character and intention is up to you. The player character is supposed to be our game avatar - a self-insert. And my intention to come to Kalos was catching new Pokémon (in this way I have a similar goal like Trevor), challenging the League and learning about the region's legends and lore. I want to befriend the region, but... it seems it's own twisted head and manipulates our player like it is a cosmic plaything. It treats you as a Chosen One for learning Mega Evolution (with the message: "To become stronger, you have to sacrifice everything what's dear to you.") while you have to earn style in Lumiose City in the hard way. So... It doesn't agree with your intentions and character unless it's the same (or similar), which... infuriates me.
This is a very interesting point, and I can understand why that would be frustrating to you in your playthrough. Although there generally has to be some semblance of linearity in order to keep the story progressing, it could definitely be an interesting approach to have a Pokémon game that allows for more individualized exploration of the region. Although, it may come at the expense of a stronger storyline, depending on how that's handled.
But I do agree that it's kind of silly, in the grand scheme of things, for Mega Evolution to essentially be handed to the player on a silver platter, but it's actually quite a challenge to become "stylish enough" to enter the Lumiose Boutique. Lysandre says I'm the "Chosen One!" I can achieve Mega Evolution! Why can't you let me buy some clothes?
I wished I could gave the Mega Ring to the rival back when we were at the Tower of Mastery... Only to see he/she got another Mega Ring in postgame while in the plot it's said there's only one Mega Ring.
To be honest, I don't remember exactly what was said to establish why the rival gets their own Mega Ring, but it does undermine the way Lysandre tried to use the Mega Ring as an example of "limited resources." "So, tell me. The Mega Ring, did you share it? ... When there is only one of something, it can't be shared. When something can't be shared, it will be fought over." But that's the only example of limited resources in the game and in the post-game your rival ends up with their own. Not to mention that Diantha has a Key Stone inlaid into her necklace before the credits roll.
The bond between trainer and Pokémon causing Mega Evolution? WRONG! The bond is necessary to tame Mega Evolution, otherwise the Mega Evolved Pokémon would go berserk! Some XY episodes showed mastering Mega Evolution is not a easy task since Korrina's Lucario tended to become berserk until she mastered it.
I have heard that the anime takes a slightly different approach to the explanation of Mega Evolution, but in my mind, although I can appreciate that the series has branched into various forms of media, whatever is in the anime is in the anime, and what's in the game is what's in the game. Aside from maybe,
maybe the
implication that Lysandre forced Gyarados to Mega Evolve (which is certainly not clear in its own right), there has never been a case,
in the games, of anyone being able to achieve Mega Evolution without strong bonds. Perhaps the lore of Mega Evolution could have been more interesting had they included what the anime did, but ultimately the anime's handling of the lore is separate from the games'.
Now to my point about the game development. According a interview the game engine for the 3DS had to be made from scratch and every Pokémon must be newly drawn AND animated. I can image it has eaten so much time there's not enough time to polish the story and characters to be fleshed out (excluding the Looker episodes, which are great), because the game engine had to be recreated and must be stabilized.
While I can understand this, at the same time I don't think it's the absolute best justification. Generally (not always, but generally) the script writers are separate from the programmers, modelers, etc. And the script writers showed they can write a good script, even if it doesn't have a lot of fancy visual bells and whistles, through the "Looker Episodes." Even if, say, the main storyline was lacking a bit visually, or if you wanted to make an argument about level design or any other area, the writing and execution of the characters is still weak. Unless the writers also work on other fields (which, truth be told, I'm not sure of myself), their output doesn't have any relation to the other groups and what they had to produce. The only thing that could potentially affect them is if there was a time issue.