First of all: vocabulary. While all receptacles are 'outlets,' not all outlets are 'receptacles.' Therefore, there is no reason to require the lighting to either be on a 20 amp circuit, or require bath lighting to be separate from other lighting circuits.
Likewise, 210.11 (C)(3) says 'at least one.' I see no reason why there could not be an additional circuit of 15 amps serving other receptacles, or outlets.
Why would one wish for another circuit? Well, my very own bathroom (circa 1940) has just such a separate circuit, to power a space heater. The other half of my duplex has removed the space heater ... and replaced it with a 15 amp receptacle. In both cases, the #14 wires are on 15 amp breakers. (Mine is a GFI
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