Paul,
Are there not different things involved here, right within Photoshop? I hardly use it for much editing these days so I may be missing something, but I recollect that for editing artifacts in Photoshop one has the choice of using the spot healing brush or the clone stamp. The former works under the hood, and as you say, the user has no control over how it blends pixels - if you don't like the outcome you undo it and redo it. Using the clone stamp however, the user must select the place from which the pixels will be cloned before cloning, and if the result disappoints, you undo it, choose another spot and redo it. The main advantage of the Lr approach is that you can adjust both the size of the coverage and the sourcing of the blend after seeing the first result without needing to undo the operation. Another interesting way of using this tool in Lr is that if you aren't satisfied with the first sourcing, you can repeat the first operation without undoing it, and Lr will itself select another blend source, which may be better. And you can do this repeatedly until satisfied. However, when I'm in trouble with this tool, which happens only occasionally, I prefer either fiddling with the blend or undoing the operation and starting over. As well, within the same tool one may use it to heal or clone, whichever works better. I'm generally satisfied with how all this works in Lr.