I don't understand why you complain. Most of the "casters" didnt have scaling spells in DotA, because they generally scaled with item actives and had better abilities overall. Meanwhile, there were heroes whose abilities scaled with their Agility or Strength.
But then again, comparing LoL to DotA is silly. We have lower cooldowns, smaller manacosts, ability effects are less extreme, mana and healthpools are much, much more larger. And this is the problem of what you argue.
In LoL, the primary source of damage is in most cases your abilities. With all the AP scaling champions, only a handful of AD champs are able to dish out more damage by auto-attacks than the scaling mages put out. There aren't many carries that'd be nigh unkillable and dishing out huge deeps once they've farmed their core items.
The reason DotA works with having auto-attack carries win games, is because they don't have a stat called AP that allows their mages' abilities to scale. As of now, the only DotA style hardcarries we have are, quite frankly, Yi and Tryndamere. Still both of them are rather lackluster in this environment of scaling casters. We dont have an item active that allows them to be immune to most of the abilities (and thus, to hard CC) for 10-5 seconds.