But all you're offering is just another setup (a more consistently contrived one though it may be) that purports to have better "execution" without any examples of said "execution" in practice (ie: like an actual story for us to look at). If the issue really is with the execution of the story, it's not really the setup you have to change, but the execution of the story in Sc1 that needs fixing, right? You can dismiss the Sc1 story all the like but you're not actually fixing the problem by starting again and rejigging the premise because that doesn't really guarantee that the story that plays out from this rejigged seteup/premise will have any better execution.
The Zerg deem the Terrans as insignificant and unworthy of assimilation were it not for this "psionic potential", so if we take that away, what else do Zerg do unworthy biological specimens they encounter along the way? They just purge them to "purify the strains". Sure, it's not a nice and engaging hook on paper but it's still faithful and realistic to the ethos of the Zerg. If you have to put a "shtick" on why the Zerg attack Terrans, you could have other mundane reasons (who said it has to be a special reason?) like gathering biomass or heck, even better, as a tactic to purposefully draw out and observe Protoss behaviour (since they respond due to the responsibilities of the Dae'Uhl) which the Overmind actually intended to do according to the manual.
Not entirely. The whole shtick of the Terrans is that they are there because they are just unfortunate. They're just there at the wrong place and the wrong time. Contrived sure? But what isn't in any fictional universe? It's no worse an excuse and less-on-the-nose than having them have some magical property that something else wants.
Well, that's real life for you, buddy. Shit happens in life and for the Terrans in the K-sector, they don't just get shit, they've got the worst and runny kind...
I don't find the magical macguffin reason any more comparatively satisfying honestly. It just makes it seem more artificial and a fiction - that everything has to have some kind of physical/inherent meaning for it to happen. That setup stuff isn't really that important to me beyond scratching my nerd interest in fluff.
What? It's there in the manual. It can be reduced down to the Zerg wanting to be constantly "better" (with their own concept of what they deem "better") and they find info that makes them believe Protoss will make them "better" (if not the "best") by a lot. So they go and try to find them.
I doubt anything I would put down would suffice since what's compelling to one is largely subjective. Afterall, the Terrans having a magical property/purity form/macguffin that is sort after by the alien menace is really just another random coincidence - it's just one that you subjectively choose to ignore as being one in order to suit your preferences.
Then why refer to them as something that Starcraft should emulate/be more like? It's why others are confused about what you want. You don't want Starcraft as it currently is to be Starcraft and you don't want Starcraft to be anything else, so just what the heck is "Starcraft" if it's not any of these things? Why not create a whole IP to meet your fanciful whim instead of trying to co-opt and force another thing into something nebulously not that thing but insisting that it still is that thing?