I'm just pointing out that there are fans who consider designs published under license to be canon in their own right, which the Loknar and Larson class were, though they never appeared on screen (a pity, seeing as how the two would also fill out the fleet nicely, and they even have their own registry numbers and everything).
I think that it is safe to say that the Saladin, Hermes, and Ptolemy are definitely good enough to be considered canon, even if under a more dogmatic definition, they might be more or less semi-canon at best.
I will admit that I don't remember seeing any screen shots showing the Federation's schematics, only hearing about it, and it seems that this might be false, since it says on the Ex Astris Scientia-Spotting the Ships from the Star Fleet Technical Manual was not one of the designs to appear on the computer screens in II or III, and I consider Schneider's website to be very accurate in that sort of thing, so I can see how the Federation class could fall outside your definition of canon. The only thing that we have canonically is that there was a starship named Entente, that was operating in as early as the mid-2270s.
However, Memory Alpha, another website that I consider reliable lists the same registry used by the Federation class of the same name, so I choose to assume that they are one in the same, and that others of the Federation class must also exist. A bit of a stretch, but one that seems reasonable to me.
I think that it is safe to say that the Saladin, Hermes, and Ptolemy are definitely good enough to be considered canon, even if under a more dogmatic definition, they might be more or less semi-canon at best.
I will admit that I don't remember seeing any screen shots showing the Federation's schematics, only hearing about it, and it seems that this might be false, since it says on the Ex Astris Scientia-Spotting the Ships from the Star Fleet Technical Manual was not one of the designs to appear on the computer screens in II or III, and I consider Schneider's website to be very accurate in that sort of thing, so I can see how the Federation class could fall outside your definition of canon. The only thing that we have canonically is that there was a starship named Entente, that was operating in as early as the mid-2270s.
However, Memory Alpha, another website that I consider reliable lists the same registry used by the Federation class of the same name, so I choose to assume that they are one in the same, and that others of the Federation class must also exist. A bit of a stretch, but one that seems reasonable to me.

Yes, the Soyuz has long been an anomaly from a starship design POV in the Trek verse. Those spire turrets could easily be omnidirectional sensor arrays. They could also just as easily be supercharged megaphaser swivel turrets. We don't really know for certain. The book "Ship of the Line" described the Bozeman as a "border cutter", complete with yellow and red flashing lights mounted somewhere on the hull as some "universal designation" as to the ship's policing purpose and intent. I could see something like that being a border patrol ship, so maybe those turrets contain both long range sensor arrays for border incursions, as well as high-powered weapons to potentially serve as a first line of defense against an invasion, buying them enough time with their big guns to get a distress message out before falling. Again, nobody knows for sure, as it's one of the least-explored canonical classes in Trekdom (next to the Wolf 359 fleet and DS9 frankenfleet, of course
).