10 years ago. They were a problem because they used American cars, clothes, weapons and media.
While the US spend lots of effort on hunting them?
Keeping the flames high, to play firemen?
I don't think that there was a need of more flames, for that theory to be plausible. Occasionally some western weapons likely did found their ways towards IS as well, but they rather captured the bulk of it. Or do you have other sources?