The only time that specifically-Joe's-Gomamon/Zudomon was directly evolutionarily connected to Vikemon in its own right was a very long time after Shakkoumon, which was in the debut appearance of the mon - which is why, to reiterate, Shakkoumon cannot be called the 'appropriator' (insofar as there is or needs to be one) in this situation.
Ukyouluvr was referring to the D-3 toy, in which all of the Ultimates were a Jogress between one of the 02 kids' Digimon and one of the older kids' Digimon (the latter from Tag Tamers or D-1 Tamers).
Paildramon + MetalGreymon = Imperialdramon
DinoBeemon + AtlurKabuterimon = GranKuwagamon
Sylphimon + Garudamon = Valkyrimon
Angewomon + Lilimon = Holydramon
Shakkoumon + Zudomon = Vikemon
HolyAngemon + WereGarurumon = Seraphimon
I always took it as Paildramon, Silphymon, and Shakkoumon are the normal evolutions of XVmon, Aquilamon, and Ankylomon and Stingmon, Tailmon, and Angemon were essentially power sources to allow perfect evolution much like the powers of the crest were required in Adventure or the holy stone for Angemon that one time in 02
my problem with the "only jogress to power up one digimon so it can reach perfect" is that why do they keep stuff from the other partner? for me their is no difference between paildramon and omegamon in concept, Koushiro even name drops omegamon after paildramon appeared, he said something like "happened before" which was a callback to the movie.
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My theory exactly
Because it the other Digimon's data mutates the original data. When the other digimon is supplying power to the base digimon, aspects of that digimon are left behind in the data, which is then used by the evolution algorithm.
Exactly, most don't reference all the base compenents for precisely that reason, some of them matter less. Also, it's less "Joint Progress" and more like giving someone a boost to help them reach the top.