Is the following tactic a sort of known debating/argumentation fallacy, and does it have a name?
Bob and Rob debate a topic. Bob provides a number of points to support his position. Some are strong. Other are more arguable and can well be attempted to be rebutted.
The latter is what Rob does. He simply ignores the strong points as if they were not made, and focuses on comprehensively showing how weak the other points are — presenting the conclusion that the overall Bob's reasoning has no merit.