Saeviomagy
Adventurer
How potent is the condition "the only melee attack that the target can make is a melee basic attack"? Against non-adjacent opponents, that is the effect of prone on most creatures.
The condition is:
1) Grant CA to melee combatants
2) Apply a -2 to ranged attacks against you
3) take a -2 to attacks
4) Flying creatures immediately crash
5) Mounted creatures must make a save against being dismounted
6) You're affected by a superior version of slow (ie - crawl 1 square is worse than movement being set to 2)
And on your turn, you can lose your move action and clear the condition.
Looking at powers, prone is rated by the designers as roughly equal to immobilize, slightly above slow and below dazed.
It's pretty good for that sort of level. It's a fine offensive debuff with some interesting secondary effects and potential defensive applications as well.
And that's all ignoring the "oh, but if I stand 1 square away, you can't attack me".
So people saying that the prone condition will be gutted if you allow an attack in that scenario are, at the very least, overstating the situation.