Slater is better than Mullins.
Mullins had a swerve, he went around people with sheer pace.
Slater has a huge step, he runs the ball back at pace, something that not many fullbacks do, and the ones who do, don't do it anywhere near as often.
Slater is above most fullbacks at present form. And to be honest the most impressive aspect of his game this season is his one on one defence. He used to clutch at the shoulders or head of an opponent and very rarely made the tackle, now his technique is spot on and his effectiveness when tackle has improved immensely.
Defence wasn't something Mullins was too good with.