Fakedit: I kinda got ninja'd but oh well
Actual edit: A lot of personal interpretation got into this, oh well. I still think that having XCOM lose the first game is reasonable and the opposite of insulting.
Dunno, that seems way more insulting. Considering things like the base assault mission, it also feels contrived. The aliens do their best to destroy XCOM. Not humanity, which they want for experiments, but XCOM definitely. I don't believe they're giving meld to XCOM on purpose, considering it "detonates" just like their weapons do. Seems more likely that they're spreading it into the environment as part of their research.
It's not like they need XCOM to unlock human psionic capability. Just look at Operation Progeny - regardless of XCOM's psi research status, the aliens instill four abductees with psionic power greater than anything XCOM ever discovers. They then use these powers to try to *destroy* XCOM HQ - not test it. They've already found exactly what they're looking for, they just need to capture Earth relatively intact.
If the player wins NewCOM 1, the aliens fail. It's true they serve some "higher power", and that could have been a basis for a sequel, but that would cheapen the victory and result in awkward power creep. The TFTD problem: All your soldiers are flying around with blaster bombs and mind controlling ethereals, so where does the challenge come from?
(Apocalypse handled this perfectly, and I would have absolutely loved an Apocalypse-style NewCOM. At least there are style similarities)
I've won games of XCOM, but I've also lost them. Heck, I haven't won it on Impossible or Long War, I probably never will. So I feel like this choice actually lauds winners. "Oh, you actually managed to save humanity despite being outnumbered, outgunned, and hilariously underfunded? That's amazing. Here's what would have happened without you, could you fix this too?"
Instead of "Your 'victory' was completely orchestrated by the aliens. More of them arrive from nowhere and delete all your research data and equipment."