I don 't think so, I 've fished jigs a bunch of times without trailer and I still catch them.
So if it's not the trailer - is it the skirt or the jig?
Gotta be the skirt, cuz if I just drop a plain jighead I ain 't gonna get a lot of bites.
What I 've found in my stay as BR member is this, people generalize a lot, also maybe it 's because I 'm old I 've seen lack of knowledge in many members which coincidentaly tend to generalize, when you say jig I don 't know why is it that you say jig aned apparently everybody makes this mental image of a rubber/silicone skirt jig :-/, man, jig skirts are not only made of rubber/silicone, they are made also with feathers ( marabou is my favorite ), hair, tinsel, alone or in combination.
Can you catch fish with a jig without trailer ? ---> aboslutely yes
Can you catch a fish with a plain jighead and a trailer ? ---> absolutely yes
Can you catch fish with a jig and trailer ? ---> absolutely yes
Can you catch fish with a plain jighead ? ---> I serously doubt it
So which one catches the fish ? the trailer and the skirt alone or in combination.
Lol @ a guy catching a bass on a plain jighead....youtube it. Of course, he used berkley gulp alive on it and it was probably an extremely "active" bass time or a severe reaction strike, but still...pretty hilarious.