lanyard reduces force on the entire system because there is no belayer. your biner is at one end and you at the other. thats how you can generate a factor-5 fall, falling 5m between rungs on a 1m length of leash.
now a screamer tied into the end of the rope isnt going to do jack squat to reduce forces on the rope system or the pro. just on you. you would fall, shock load the pro, then the screamer would rip and leave you hanging 2 feet lower.