Better go back to the library, the old memory ain't what it used to be. While Meredith's Brigade deserves its laurels won at Gettysburg, it's delusional to say they kicked butt. In buying time they were effectively destroyed, losing 1153 of 1829 engaged and, finding it impossible to recruit quality replacements, were never a factor again. Their first fight at Gettysburg against Archer was against one of the weakest brigades of Lee's army.
If losing very nearly 2/3rds is kicking butt, what would you say counts as getting whipped? A shorthand 19th Century method of determining the victor was to note which force held the field at the end of the day. The Iron Brigade after all their efforts marched back through their own footprints.