but he was taken down by Frankie. Wouldn't the 170 pound grapplers maul him?
Frankie's takedowns were largely predicated on timing, technique, and speed, all three of which is he in vastly greater quantity than any top welterweight. I think the Thomson fight is a little more worrisome, and make me feel like Hendricks, possibly McDonald, and especially Lombard might be able to score takedowns pretty easily in the clinch.
Despite that, I feel like the time is right for Benson. He's not about to get any real shine at LW, especially with Pettis as champ. Welterweight feels a bit weak right now. Worst case scenario it doesn't go well and he drops down, possibly with a champ people would have more interest in seeing him fight (Khabib, presumably). Best case scenario he may make a real run. Benson has consistently been moving towards a more speed-oriented outside point-kickboxing game, so a speed advantage may do more for him than a strength advantage. He's also hard to hit, and generally good at looking like he's the more active fighter. Considering Lawler, McDonald, and Lombard all have a tendency to pursue 5-minute staring contests with their opponents and Hendricks's gas tank is all over the place, I find it hard to imagine them matching his output. They may need to either take him down and keep him there with the cardio to do it consistently or get the KO.
Of course, the top 4 certainly have the power to get the KO, even McDonald, and Benson's boxing has always been wanting. I don't think I'd favor Benson over any of them. But if they spend too much time mesmerized by his movement (or gassed, in Hendricks's case) and start letting him steal too many rounds, I wouldn't be shocked.