No, the scimitars are not a waste. They do work. There are a couple of APC props that seem to be the "go to" prop when nothing else work. When flying the larger models, line tension is your friend, and the prop has a lot to do with that. So does the altitude you live at! And the size and weight of the airplane. The APC and most of the off the shelf props are relatively inexpensive, so you can try a couple of different props as you go, then store the rest until next model. Then the process starts over. I have a big box or two of props from all the years I'v done this, and won't throw any away or sell them, because you never know when a certain prop might just be the ticket. I tried some Zinger Pro props with the scimitar shape on a couple of different engine/plane combinations, and just wasn't impressed. I put an OS.32 on my P-Force a year or two ago and started the prop dance to find what felt best, and the Zinger 11-4 Pro that didn't wake me up on other airplanes, was just the cat's pajamas on this model. I think you have the basic idea about the impotance or lack of on tip shape, but just to illustrate again, I was looking for a better prop for my Shark45 but in a smaller diameter so I could use shorter landing gear. I was using an APC 12.25-3.75 but wanted to get down to close to 11 inches in diameter. I made a tracing of the tip on one, cut it down, and carefully reshaped the cut-off tip to restore the original shape, and it seemed to work OK. Then, at a contest, I needed another one, and didn't have the time to goi through all the work of reshaping, and just cut it off square and accurately, balanced it and went flying and it was better!. Doesn't look as nice, but I don't worry about that as long as it keeps me from having to do a lot of back peddling with the airplane at 45 dgrees! I guess the short answer is, just get your hands dirty and see what feels good and performs the way you want it to. It's not always strictly about RPM on the ground, but how it feels and performs in the air.
Have fun,
Dan McEntee