Friz, Brodie, Croker, Cant, McEwen and especially Lucas & Elijah SL are all more mobile than average for their position. The only player in the pack who'd be less mobile than an average player in their position is Kai.
The issue guys like Cant and Croker have had isn't around how well they move, but physicality. I love Croker but he plays "smaller" than his listed height/weight, and relies on late footwork to help us generate go forward. Cant is willing and rarely actually misses his defensive assignment, he's just getting absolutely killed in contact (which is why it's all the more baffling that we try to get on the front foot with direct one out running, when you have a clear size disadvantage you need to frontload energy into line speed and then in yardage force the defensive line to move laterally as much as you possibly can & switch to punching it through the middle only once you've put fatigue into the defence. Which I know is easier said than done and no one does it as effectively as Penrith, but you have to at least try... trying a power game with no power runners is just conceding defeat).