The problem with 3.5/PF (I have no experience with 4) is that there was essentially no limit to how powerful your character could be. You could find/create all the stat boosting items, multiclass, slap on templates and end up with 40-50+ in your primary stat while not even hitting "late game". Not only that, but different (and a few same bonuses) stacked, making attack/damage rolls absolutely ridiculous. In 5e your stats are hard capped at 20, with very few items (mostly/only strength iirc) allowing you to go beyond the cap, but ONLY with that item.
5e isn't going to get "overburdened" with splat books. Aside from Volos (which is limited in the character options it gives), since the release of the PHB, only 1 "Splatbook" (though half of it is lore fodder) has been available in the 2 years and nearly 5 months since the PHB was available. WotC has been dedicating most of it's time releasing campaigns for the system than anything (6 in the same span of time)