Messing around with Scraps had me pull out this old staple: Dark Melee/Shield Defense. HONESTLY, it's tough for me to think of a more synergistic pair, and really I don't know if there is anything in the game that it can't do/wouldn't be a good addition to a team for. They go together like peanut butter and jelly. So, as the OP said, a true "One Scrapper to Rule Them All." Also, my caveat: I'm not saying that it is the absolute very best in every scenario. I'm just saying that the scenarios where it wouldn't be a good choice are few and fair between.
For my build, I have all my positions softcapped for defense, but I'm also running body mastery for focused accuracy and physical protection. While both are good, idk if I'm leaving too much damage on the floor by not having a snipe. If any others have builds they'd like to share for this combo, I'd love to get some ideas/see what ways you went about building it!