The rules are unclear about this. Page 16 of the How to Play document says:
And yet, on pages 4-7 of the same document, Strength and Dexterity state that they are added to attacks and damage for melee and finesse/missile attacks, while the Magic Ability description (for Int, Wis and Cha) say that the modifier is used for attack rolls and DCs, but damage is not mentioned.
I suspect that the former is a copy and paste artifact, since they deliberately removed the mention of the ability modifier adding to spell damage in several other places.
Rogues are worse at fighting than Fighters? Sounds like that's working as intended. (Seriously though, "target must be within an ally's reach" is not much of a restriction.)
Fighters and Rogues were always both good in combat, but in different ways. Fighters tended to hit more reliably, have more attacks, and more feats (in 3e), while rogues had backstab/sneak attack that enabled them to do more damage than fighters when fighting dirty. Now, they have no advantage over fighters at all, not even when they are ambushing their foes.
Besides, I think it's important that the various options for combat expertise be balanced with each other. One should not be simply superior to another. You'll notice that rogues and fighters share several maneuvers. Why should those be balanced with each other but not deadly strike and sneak attack?
A level 0 cleric spell is worse than a level 1 wizard spell?
Ah, I didn't notice that Magic missile isn't a 0th level spell anymore. Thanks for pointing that out.
You're really exaggerating here. For one thing, level 6 wizards are not going to be casting sleep. They are going to be casting 5d6 fireballs and 6d4+15 magic missiles.
Only twice per day. The rest of the time, he'll be using weaker spells or cantrips. 1d6 + 3 damage rays of frost are pretty sad compared to a fighter's [W] + Str bonus + 2d6 (at level 6). With a two-handed weapon and an 18 Str, that damage is d12 + 4 + 2d6, or (7-28, avg. 17.5) damage. A fireball does 5d6 (5-30, avg. 17.5) damage. The average damage is the same, but that's the wizard's highest level spell (3rd level) at level 6, and he can only cast two per day! The rest of the time, whether using lower level spells or cantrips, the fighter is far out-damaging him. I don't think that's right.
I agree the fighter should have some advantage since he doesn't have daily resources, but his at-will attacks shouldn't be as or more powerful than a wizard's daily spells, and they certainly shouldn't be so much more powerful than a wizard's at-will spells that they leave him in the dust, IMHO.