I find the Axis and Vector combo to be the perfect mid setup. Right now I carry a pretty domey FR Vector with a healthy amount of fade and no high speed turn, a mild dome axis that's like -.125 HSS and 1 LSS, and a flat fairly worn axis that's like -.5 HSS, .5 LSS. Since I utilize forehands a ton for close range shots I don't feel the need for anything flippier than my flat Axis, and I have a beat to hell JLS bagged anyways.
As far as the Ion and Anode go I do think there is more overlap between them, but not so much that it isn't worth having both molds. I think one reason some people might feel this way is most players don't use a putter outside 100'. I play a lot of putter rounds and drive them almost 400' these days so when I throw Anode's and Ions back to back in the 300-400' range, I do see a big difference. All of my Ions like to fade. Some earlier and harder than others (Looking at you, max weight opaque non textured Ions) but they all want to have 0 HSS and fade a decent bit at the end of their flight.
My Anode's do not behave this way. They are much more neutral at any distance, and hold the line I put them on more than the Ion does. This makes them a superior putting putter, better for touch shots and tricky approaches, and makes truly straight drives easier to manage than the Ion. I think the Ion can be easier to range since it has a more reliable fade and less glide, but overall I prefer the Anode for anything I would use a putter for, whether it's a 40' putt or a 350' drive. I think it's good to have one of each in the bag if you use putters as drivers a lot, but if you're like most people with putters one mold is probably all you need between these two.
Here are some videos to illustrate the differences. The drives are much easier to follow if you fullscreen in 720 or 1080.Anode showing minimal fade on a ~60' puttIon showing slightly less glide and more LSS on a similar puttAnode being driven pretty straightAnode being driven even straighterThis mild hyzer flip to flat drive would of been impossible to do with a current style IonThis flex shot at 365' would of been impossible with any kind of Anode on the market. Notice I throw it with anhyzer and it still fades back considerably.