I know II is held in high esteem - a cult favourite at least and an out-and-out great album for some.
I think it's overrated.
As someone who is a big fan of
Queen II, I disagree with you, but understand what you mean.
Queen II is a fascinating document of a band that is still finding itself. When the debut came out, the band was dissatisfied, because it had taken almost a year from recording to release, and they had significantly evolved since then. Hence, they did not feel it properly represented them and their style anymore. Like many debuts, it was a collection of songs that had been developed and refined over several years, tried and tested live, and thus the album seems comparatively tight and structured.
Queen II is a mess. But that, I think, is what is so great about it. You can hear so many brilliant ideas that are not yet dealt with in the disciplined manner of a professional recording artist. On the one hand, it makes you wonder what would have happened had they decided to further explore a certain set of ideas or continued on this or that avenue. On the other hand, you can hear masterpieces in the making. What is
March of the Black Queen if not an embryonic version of
Bohemian Rhapsody? This song deserves much more attention as a document of the development of musical ideas. Freddie reportedly had been working on
Bohemian Rhapsody since the late sixties, and I think this is the first time he tried to shape his ideas into a coherent song. It is certainly not as coherent, refined and composed as
Bohemian Rhapsody, but it's a remarkable glimpse into the mind of a genius nevertheless.
I think your remark about the Brian and Freddie sides is true to a certain extent. It presents both songwriters as distinct individuals, and it probably does help to appreciate their later combined efforts, although both remained prolific songwriters of their own. Many of Queen's most enduring classics were written by only one of the two (or neither). Again, this presentation of the album allows for a unique glimpse into the development of the band. I guess it boils down to whether this is what you want to appreciate in a song or an album or not. Generally speaking, I probably wouldn't care enough for it. But in the case of Queen, investigating and exploring the individual threads is just as fascinating as admiring the whole tapestry. I think this is why
Queen II is so popular and admired among fans.