In my experience, your statement that using a bushing die with an expander in place is a waste of time is incorrect.
If you size an UNTURNED neck with the typical one piece die, the case neck will be reduced to the extent that if the die's expander is used, the friction will cause so much pull on the case that the shoulder would yield asymmetrically, cocking the neck in relation to the body.
On the other hand, if you size a similar case with a FL bushing die, a busing can be used such that there is hardly any pull at all, and concentricity is not degraded. Also, if the standard expander does not create enough neck tension, it can be reduced in diameter so that it does, and a smaller bushing used with it. This is not theory, or conjecture, I have done all of it.
Additionally, if one is forced to use a one piece die, and wants to get the best possible results with unturned necks, cases can be sized without its expander, leaving their neck IDs too small, and then expanded using a expander die and mandrel and die, designed to be used to prep cases for turning. This results in straighter cases than if the die's expander is used. I have done it both ways.
Of course if you are going to turn necks, it is important that necks be expanded with a expander die, and a mandrel that is sized to produce the proper neck fit of the neck on the turning mandrel.
With all kinds of expanding, except that producing the very minimum of expanding, lubrication of necks' IDs is called for, and the rate at which the expansion is done is related to the pull on the case. Take your time, and there will be less pull.
Added a little later:
The following is a link to a review of Whidden reloading dies.
http://www.accurateshooter.com/gear-reviews/whidden-gunworks-sizing-dies-and-micrometer-seaters/
If you read down the page a bit, you will come across the following.
"One other very cool feature of the Whidden sizing dies is that custom-sized tapered expanders will soon be offered. Whidden plans to offer expanders in .0005″ (one-half thousandth) increments. This is great if you have, say, a .265 bushing and a .266 bushing but you want just a little less neck tension than the .265 offers. With the tapered expander, I can use a 0.265 bushing followed by an 0.2655 expander — allowing more precise control of neck “gripâ€."
If his name does not ring a bell, here is a little information to introduce him.
http://www.nrablog.com/post/2014/01/15/NRA-Long-Range-Rifle-Champ-John-Whidden-makes-the-rounds-at-SHOT-Show.aspx