We create one. We, the community, discover which guns work well(in our opinion) and we use them. Exclusively. The problem is that we then refuse to branch out and try new things because we've become comfortable with what we consider the "best" options.
You want a change in the meta? Explore your options. Try new things out. I've recently been experimenting with Lord of Wolves, and I've found that it's a great gun, just as an example.
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So...what is the meta? I find most things pretty effective right now. Pretty much any weapon type with a good roll seems to work...