I dont think chart position comes into it when the record is 20 to 30+ years old. Being underrated has nothing to do with sales but the longevity of the record. With the exception of Band on the Run, most of the Wings material is thought of as average.
When you compare a record like Ram to Plasic Ono Band, Imagine or All Things Must Pass then you can say that it is underrated as the quality between these 4 records is hardly huge (i'd say that all are between 4 and 5 stars depending on the individuals personal preference) and they all charted high when they were first released, but from the the music media Ram is never mentioned as a solo beatle great while the other 3 with BOTR are always mentioned.
I dont know why your so upset with someones opinion of whats underrated, if you dont agree just say so no need to compare peoples thoughts as 'weasel' like.
Tug of War is and was called Paul's masterpiece by most. Band On The Run was called the first album by an ex-Beatle worth buying, and the public confirmed it's love for this album when the 30th anniversary compilation actually re-charted. How are these albums "underrated"?
As far as your album comparisons go, consider something. The Beatles broke up, and riding high on the Beatles momentum, John and George put out a couple of good albums. But that was it. After the momentum died down, their output was quite average. When you get down to it.... there is nothing particularly adventurous in those first albums. It's just good, safe, middle-of-the-road please-the-masses guitar rock. One of the reasons BOTR is so highly regarded is BECAUSE it is the closest Paul ever came to safe, middle-of-the-road guitar rock. You'll find that the further away his 70's albums were from this, the worse the "ratings" for that album got.
A quick Google search confirms that theory. Notice how the 70's albums that are less middle-of-the-road guitar-rock oriented (*) generally fare less favorably:
McCartney 4.1 out of 5 stars
Band on the Run 4.5
* Red Rose Speedway 3.5
* Back to the Egg 3.9
* Venus and Mars 3.6
* Speed of Sound 3.5