To try and condense the discussion instead of replying individually to everything, my main points are:
Weapon:4 and 5 should be a big deal--the game treats them as such, with Weapon:2 being considered lethal force.
You already have a stress bonus for using a given weapon--the weapon's own weapon rating. These kinds of stunts feel like double-dipping to me, getting two bonuses for one condition.
Most combat stunts, in particular ones that grant a bonus to attack rolls or to stress, are situational--which is to say they are dependent on factors that are largely out of the player's control--things like the numbers of opponents, the armament of the opponents, etc. These stunts are dependent on something entirely in the player's control--what weapons they choose to go into a fight with.
Other stunts that create such substantial bonuses to stress and attack are either in limited situations (Lethal Blows only really works on something without any armor rating), or with some kind of penalty (Berserker limits your actions and comes with a penalty to defense).
These stunts, and others like them, run contrary to how the fiction is portrayed even within the rulebooks. In the fiction, and without these stunts, even a Submerged level pure mortal will have to pull some tricks to beat a Ghoul one-on-one, whether those be spending fate points or maneuvering or blocking. With these stunts, a Feet In The Water pure mortal--which is, per the game's description, someone who has just started to get into the supernatural world--can take on a Ghoul and has the fight largely in his favor without having to spend any fate points or maneuver at all.
Ergo, something that helps create such a large disconnect between one of the stated intentions of the game (emulate the setting accurately) and the result means that something is wrong with those stunts.
I can see having maybe a +1 to stress for a specific weapon. Or having a stunt that gives you a bonus to creating blocks or maneuvers with a specific weapon. But, to me, doubling or nearly doubling the weapon rating, having a flat +1 bonus to all attacks, and a flat +2 bonus to all defenses all under the same condition--a condition that is entirely within the player's control--is just too much.
Maybe that's the ticket--treat the "don't stack stunts" thing both ways. Not only do you not stack stunt effects, but you shouldn't stack stunt conditions either. Having several stunts combining for a massive bonus to fighting ability all dependent on one (easily forced or met) condition creates an imbalance.