I have some doubts about the Valentines and Justice: 1)Considering what you said about Dizzy's Gamma Ray and Necro Install, how is it possible that at least two of the Valentines (the one from GG2 and Ramlethal) have the Gamma Ray ability and the mind control over the Gears (the one from GG2) if they aren't Gears?
First, understand the nature of weapons in Guilty Gear… how they can be built and replicated. While the output may not necessarily be the same… weapons are weapons and can do damage just the same. The name might just be a deliberate means of throwing us off the trail of speculation on who’s related to whom, after all… even something like Sol’s Junkyard Dog can emit a powerful beam of light not unlike Justice’ Gamma Ray… and considering Sol’s “Dragon Installed” Tyrant Rave… if he can do it, who’s to say anyone else couldn't manufacture that kind of power artificially?
Further, understand the nature of Valentines and Gears…:
Valentines obey Mother… they cannot disobey her absolute orders unless something happens that causes them to resist against them:
Valentine: "What Mother wants…doesn't matter anymore!"
Elphelt: "This is the only freedom I have left… If this was how it was going to end… I wish I’d never been given emotions… If this is all they lead to… Why did I have to have feelings anyway?!”
Justice: "I see…Unlike the other Gears, I knew he wasn't completely mine… Feelings for his parent… Love… I suppose… He still felt such emotions… Perhaps, in his diseased mind… He thought he was doing all this…for you. Now… I understand… why my… power… was… limi… ted…”
If there is a difference it is this:
Life when it is born, naturally and slowly develops “emotions”, “identity”, and “thoughts” of things beyond its own self. You could call this a breakaway from a theoretical higher consciousness (not to be confused with the so-called ‘Universal Will’ that the Conclave talks about, but something like it). The ability to make choices seems to be something that only certain individuals possess, be they Human, Gear, or Valentine.
Valentines can be born and “programmed” with or without emotions, much like Gears… but unlike Gears, Valentines are closer to being “Human” because they have blood types and because they are “born”, whereas most Gears are either “created” or “converted” from other forms of life. Sin and Dizzy are rare exceptions because of their “Quarter Gear” and “Half Gear” statuses and are closer to being human as a result. Human conversions like Sol and Testament are also closer to being Human… even if they are still Gears, though, despite that, their blood cannot be analyzed for some unknown reason.
Upon further analysis… while Valentines can “develop” emotions… those emotions cannot circumvent Mother’s orders… unlike Gears who can ‘evolve’ past the need to obey orders from a superior Command Type Gear. As a result, unlike Gears, Valentines may develop a split (albeit difficult to define) consciousness, as was the case with Elphelt.
Then of course there is the founding idea “That Man” placed in our heads about the Valentines being “illegitimate heirs”.
You could say that a Valentine is closer to being a rough "Copy" of Justice than being the genuine article. This also further illustrates their need to ‘revive’ Justice, over attempting to replicate her, because of the power the original Justice had.
Does that mean that Valentines are Gears? Or does it mean that Valentines are Human? The latter seems more likely, given the Valentines have been unable to defeat Sol Badguy (the Prototype Gear)… but it also means that the Valentines wish to become like “True Gears” in terms of strength and power… so they try to replicate and imitate the power of Gears.
Though Valentines are “closer to human” they are still ‘not human’ because of their powers which are comparable to Gears, and their inability to express emotions or understand humans… but that could change in the future, assuming Valentines have the capacity to evolve like both Humans and Gears do…