gaelicspirit writes very good capable, intelligent, BAMF!Dean while keeping it all very believable. Try these:
Night of the Hunter (http://gaelicspirit.livejournal.com/136953.html) - Missing scene from 5.02, Good God, Ya'll through 5.03, FTBYAM, leading to the first part of 5.04, The End: This story chronicles what Dean did and went through during the time he and Sam were apart. Starts from when Sam walks away from the picnic table and ends when Dean gets back from the future. Let's just say there are vampires, a werewolf, a case of mistaken identity, some sleepless nights, a lonely man, and a lot of Dean.
Wake Up and Fight (http://gaelicspirit.livejournal.com/121706.html) - Season 5. When Sam is attacked and marked for possession by a 'Hell Bearer,' Dean will stop at nothing to save his brother. Pain and exhaustion he's handled before; however, adding to that the horrific memories of Hell may be too much for this world-weary hunter to bear.

alexjanna91's Adventures in Babysitting (Apple Pie Life) (https://archiveofourown.org/series/36906?hide_banner=true) has Dean showing his gentler side with kids, and the last installment also has BAMF!Dean. - Dean had promised Sam he’d try living an apple pie life, but he’d had no idea it would be so freaking perilous. Smart-ass kids, helicopter moms, asshole husbands, creepy dudes in the park, and more drama than a daytime soap-opera abound. Dean’s stuck wondering if he wouldn’t have been safer sticking to hunting.