The Raichu pose is similar to the Base 2 pack.
And the fact that they're 3D really does make them fall flat in mirroring the Base set (and Base 2) pack art. I honestly don't know if this would have been a tall order or not, but why not ask Ken Sugimori to revisit his old artstyle to recreate the megas in the same poses and style of the original artwork for these packs? If he doesn't want to do it, there are other talented artists who CAN recreate his old artstyle. (Though, I'm not sure what you do about Raichu, in this case, to make it different like the others. Alolan Raichu? No, this is still an XY set...) When I saw the pack art for Evolutions, my immediate thought wasn't "It's just like the original poses!" It was "Oh, neat! That's what the packs will look like. ...The end."
I can't help buy feel like this was done in order to keep the children's interest with the flashy 3D Pokemons and such. Meanwhile, it probably would have been beneficial to have that old-style artwork in order to capitalize on all the nostalgia going on for Pokemon between the 20th anniversary and Pokemon GO. Didn't that Base set reprint "story" from much earlier this year get A LOT of attention? Imagine someone who is playing Pokemon GO, who hasn't played a game or bought cards since the first gen, and they see these new packs and they instantly remind them of the Base set packs because of the old-style artwork. "Oh, this is neat! You know what? I'll buy a pack or two." And then they see all of the old artwork on the cards. Maybe they get a Charizard, or a Venusaur, or a Blastoise, or Mewtwo holo. "Oh!! I remember this!" Or maybe they get an EX. "Whoa!! What on earth is this craziness?!" Maybe they'll decide to buy more packs, and maybe that will lead to trying PTCGO out or maybe even going to a Pokemon League. (I know that all might be a bit of a stretch, but it could happen.) But with the Pokemon pack art being 3D the way it is, you'd more likely have to explain to someone that they're similar to the Base set packs, only to get an "Oh, yeah. You're right." reaction.
(Edit: I just think these packs were a missed opportunity.)
I don't hate 3D art; it takes a lot of talent to make it look good, which this does look good. ...But it's just so boring to me compared to hand(tablet)-drawn artwork. Let's just use the XY sets as an example. The first four sets. 3D stuffs, I honestly can't recall the artwork on them that well, but Flashfire's colors were nice and bright. The next three ORAS sets--holy crap! Awesome artwork on all of the packs!! I remember every single one--especially that Mega Gardevoir artwork!! That background, the moon and the stars in the sky, the Pokemon itself!! So good! Then the BREAK sets. WE ARE 3D MODELS ON A 3D BACKGROUND. THAT IS ALL. SNOOOOOORE. In terms of artwork, my favorite packs (outside of Japan) are the HGSS era and ORAS packs. We need more like those.