Reading through this, I finally figured out why there feels like there are so few left-splays in the base game: Because so few cards have them! (I have personally never gotten Wonder via Invention)
The only cards that splay left in base are Code of Laws (slow), Philosophy (slow), Paper (decent, except that the other left-splays are kind of bad, otherwise it'd be really good), Feudalism (just plain bad esp. in a 2p game), and Engineering (situational). Compound this with the fact that your piles can often be only one card deep (or non-existent) early in the game.
Not to mention Invention's second effect is kind of unsynergetic with its first: If its second achievement-claiming effect wasn't there, you'd probably still get Wonder pretty soon once you've gotten your left splays to face right.
(shameless bump because I refer to this topic a lot)