Years back the foot lock made perfect sense. The bit of rock that held your foot in place has long departed and knee pads are now accepted attire. I'm sure I've done the move since without assistance. The slopper was always an intermediate hold for me. I'm also weak. Persistence is needed. You'll get there. Great route.
I dont recall the exact details, but I did it with beta similar to yours, going left hand to the crimp rather than going again with right. I think it involved a bicycle with feet to work and was a very fast slap.
I remember the footlock being useful (stops you flying off when going again with RH maybe?) and it feeling about 7A+ish. I don't remember much else though, and it was before I had realised that knees existed... Vid of Moon doing it: Vid of Haydn with different sequence:
Cheers! That photo is interesting as it is toehooking an undercut i hadn't considered.
The intermediate is a decent 2 finger crimp just down and left of the sloper.