EXP Share kind of needs to be turned off if you do not want to steam roll things; I turned it off late (Gym 6 or so), and levels did end up lower than the E4 at least by the end! I think of the EXP Share as a difficulty modifier of sorts rather than a feature. Game letting you turn it off whenever you want to me makes it, at worst, a poorly implemented object that you ignore, rather than a legitimate flaw.
Think of it as analog to things like FF9 Tetra Master, where in if you don't like the feature, ignore it and pretend it's not there; game does not penalize you for this.
Elfboy, fwiw, Gen 5's battle speed is about even with HGSS (which is a significant improvement to DP; sounds like Platinum is about the same.) It does, however, do a few things that speed the game up in general. The one that comes to mind is weather; it will only show the weather effect the turn it is activated, then have a symbol in the corner reminding you what weather is activated when selecting commands, so you don't have to go through "Rain Continues To Fall!" *animation* every turn. XY naturally did something similar.
But yeah, XY is one of the faster Pokemon games, even though it sounds like it should be one of the slower ones. Gamefreak really did a good job in that regard.
Giga Bowser RPG: So I had a bunch of useless plumbers beat up a Bug/Fairy type Caterpillar by abusing some ruler mechanic! Also our hero punched a giant tower mech a bunch of times.