KitBashing has variances in difficulty which makes the distinction between them hard to pinpoint, but the distinction is there. You have to look a the history of the terms.
As people have said Kit bashing means it is bashed from several model kits. Taking the front of model A, the back of model B, and maybe the wings from model C and making them one distinct model. For the 12" Joe customizers this meant buying several different figure sets or accessory sets and combining pieces from each to create an entirely new look. For modelers a kitbash takes time and work to make those pieces work together. For 12" Joe customizers it takes time to accumulate those parts and the vision to see the different accessories to create that new look.
Now fast forward to Evilface's site and Zarana-X coining the term with a submission description which had minimal effort to it. For ARAH customizers, we only needed a screw driver to do a kitbash. While part swap customs are still cool, they are also pretty easy. LBC just kind of stuck for those simple customs. It isn't a knock against them. The term just acknowledges it isn't quite as complex as something that someone spent 15 hours painting super detail camo on.
As drbindy said, kitbashing has become just customizing in general. However you have the Club which has called the ARAH kitbash/part swap customs FrankenJoes.
So, you can have a lot of different people calling them different things based on how they came into the hobby.