Standard dies are designed to put enough sizing on the thinnest neck the cartridge drawing allows for. The average neck is thicker and is over-resized by it, so the expander is needed to correct for the over-resizing. From the SAAMI drawing, the neck has a 0.004" thickness tolerance, which is 0.008" in diameter. That is, the neck over a seated 0.2644" bullet can be 0.289" to 0.297". Since your case necks are 0.296" before resizing, and allowing for 0.001-0.002" of spring-back from the chamber size, your chamber is not loose. It will accept maximum diameter cartridges. The die is designed to reduce a 0.289 case with a -0.004" thinner wall and have it spring back out some. You are correct that this overworks the brass. How much depends on your actual wall thickness. The best way to find that is to measure the neck over top of a loaded bullet whose diameter you have measured before loading it.
There are four cures.
One is to get the neck of your sizing die honed out by the 0.008" to remove the extra steel (assuming you aren't going to change to a different brand of brass with a different neck thickness later). RCBS and Forster both offer this service for their dies, IIRC, but I think RCBS only does it when you are ordering a new die from them.
A second approach is to buy a neck bushing type resizing die and buy a neck bushing the right size for the neck to come out only as wide as you need it to be, thus only lightly rubbing the expander. Indeed, you really need no expander with this unless your case mouth is dented and needs rounding on the way to the neck bushing. Even then, the next size smaller expander is usually adequate for dent removal (a 6 mm expander in this case).
The third is to use a Lee Collet Die to size the neck separately and a separate Redding body die for resizing the case below the neck in a separate step.
The fourth is to outside turn your necks down by 0.004" to fit them to the current die. That's more brass removal than is normal in one step, so it might take several passes and does weaken the neck's hold on the bullet, altering start pressure. It is the least attractive of the alternatives to me. Also, thinner brass will expand more in your chamber, to the amount the brass is being worked doesn't change; just the direction of it does. But it will lessen the expander drag.