I do not see that as a problem for in fact that being MAF can sense humid air and adjust for it assures the PCM is properly adjusting for the quality of air.

PCM is not a perfect realtime monitor and adjuster since it only has to make changes over time and as long as PCM keeps AFR to within 1.5 times the FTP ( Federal Test Procedure) rate then all is well.

Really having the fuel trims ramp up/down (rich/lean) is good for that assures the O2s are properly also ramping above and below .450 mVolts.
If fuel trims stayed flat then O2s also would and that would confuse the PCM thus as long as STFTs are within that +/- 5% then engine is running perfect and forcing flatline of fuel trims would not make any more performance.

Take a simple driving up and down a hill, if PCM was realtime the trims would be lean, then perfect 0 and then rich going down the hill. If PCM realtimed those changes the engine would not run smooth that driver could feel and why PCM only reacts to LTFTs once every 10 minutes and once a second looking at O2 values.