Why would BP be stronger than Cap and Bucky? They have SSS, and anything above that is superhuman, right? I might be mistaken cause I don't read comics, BP isn't a superhuman, is he?
I don't mind BP looking awesome, but I want Cap and Bucky to look awesome too.
Typically in the comics T'Challa and Steve Rogers are physical peers.
Steve is typically portrayed as being a bit stronger, but T'Challa is much more faster and agile. T'Challa also has enhances senses that border on superhuman.
A common mistake I've noticed people making is assuming Panther gets his powers from his vibranium mesh suit. The suit (which is a ceremonial garb and not really a costume) is made of a vibranium mesh, and that pretty much makes him bulletproof.
In the comics Panther also has special boots with Vibranium soles that allow him to run up walls, fall from great heights but land safely and silently, and on one occasion actually walk on water.
T'Challa gets his powers from a heart shaped herb (which gives him a connection to the Panther God Bast). It's basically mystical version of the SSS+Vita-ray bombardment.
In terms of fighting skills they both have unique styles they've developed over the years which are mix of various martial arts styles. Unlike Steve, T'Challa has been trained since birth.
In the comics whenever the two fight it typically ends in a draw (there are a couple times where on wins over the other).
In the film it definitely looks like T'Challa is faster than Cap and possible just as strong as him.