I've flown with both and against Willie. They are good pilots. I was in a TDM with Evilwillie and I got focused hard but he was able to get top kills (we still lost) and I think he was solo queued. I saw Sleeth as a teammate in a domination match. He got focused hard with 2+ always chasing him around. He was still top 3 in kills and we won.
Same observation here. I'm not 100% sure, but I seem to see Larrah with them a fair amount too. Regardless, from my experience, they're all good pilots individually, but their teamwork is a big force multiplier. As a team, they're tough to beat, I can't say I recall having been in a match when they've been on the losing side. Kudos to them, they've got skills and good teamwork to match.