I understand your opinion, but there is no "worse" in terms of what the pokemon will do, everything is made with a purpose and is not useless or worse compared to something who is made to do another thing. All is usefull and equally important. However if the question would be like what is the best speed damage dealer? Even then it will have to take into account many factors including types, the particular enemy you will use this pokemon to conter against, movesets, stats, and even the majority of enemy types that appear. For exemple, against a grass type, Skarmory would be the best even having less speed than swellow because is 4x more resistant to grass moves, beside having flying moves and being faster than most grass pokemons. However in terms of neutral enemys and majority, swellow would be the best to suit this "particular role", because is faster than skarmory and can hit most pokemons first in general. I'm not criticizing but even then that are alot of things to consider, have all a nice day. :)