My take is that a plugged fuel filter would likely cause the engine to starve/stumble under acceleration rather than give you poor mileage.

If the MAF looks good that doesn't prove it is ok. However that and the fact you are only getting one bank with a CEL would make me look elsewhere.

Depending on how tough the sensors are to reach and how stuck in place they are I would strongly consider swapping B1S2 and B2S2. If the problem moves that says sender to me.

A leaking intake manifold gasket would also give you the CEL. You having a surging idle problem? If so that says IMG problem to me.

The CEL will turn off after three trip cylces where it isn't tripped. It will clear memory after 40 trip cycles.