If you eliminate at-wills and grant more encounter powers to make up for the decrease in effectiveness that will cause, it makes hitting with those new encounter powers that much more important to prevent over-extended, grindy combats. I think you'll still see Clerics pumping their Wis and Str to the detriment of their Dex because Str and Wis are the stats they need for hitting with their more-effective daily and encounter powers. A Cleric, under your system, that gives up one of those stats to have a decent Dex so that they can have a chance of being effective with their basic ranged bow attack is doing so at the cost of missing more often with the encounter powers you are relying on to balance out the loss of at-wills.Removing at-will powers opens up design space for character types that are currently sub-par by the RAW. It doesn't matter if you are martial, arcane, divine, primal, elemental, shadow, ki or whatever other power sources they are going to come up with. Characters are limited by the at-wills that they are tied to at character creation.
This makes having characters that do not fit the mold of those prefab at-wills outside the ability for the RAW to deal with and a limitation of the game system.
The perfect example is the elf cleric archer of correlon. This character is not a very viable build. I mean, what would a cleric be doing with a bow let alone a high dex. A ranged cleric is a lazer cleric pure and simple and that only requires uni-pumped wisdom to be effective. With making basic attacks the standard instead of lazers it says, "Ok I can make an archer cleric because I am not losing anything for doing it." Thus it opens up many more character concepts that were previously unavailable.
I think the much better solution here is to just make up some at-will powers that exactly fit the archetype you're going for. If you want an archer Cleric of Corellon, just create some new at-will powers that feature AC-targeting archery damage rather than Will-targeting radiant damage. As long as the archery attacks are still Wis vs. AC you won't be changing any of the assumptions of the game, but you'll have the flavor you want.