So, ah, how would a person who is above-average prove they're in a "sufficiently committed" relationship?
But I can easily see how it'd go wrong. If you spend your visits impersonating rabbits, what proof do you have? If you spend more time on snapchat than the phone, what proof do you have?
There's an old trope of "yes, I do have a girlfriend. you wouldn't know her, she's from another school." She lives in another city, she's from Canada, etc. How do you expect your friend to prove their claim? Now replace the playground with INS/USCIS.
It ends up being a very vague question because there's no set limit of what level of evidence you need to reach, you just need to "satisfy" whoever opens that file.
The second time, I wrote a photo-story instead of just packing in a pile of 4x6 prints. "Here's us dating, here's us married, we took this trip here, this other trip there, here's my partner and her child with my parents and one of my siblings, here's me meeting her parents, here's our wedding, here's me and the kid, here's all of us at various events, here's us celebrating an anniversary," etc.
Same address (and checked by immigration official) means you already have a temporary visa. (Same address in another country does not count, easy to fake.) So they already let you in...
Having paid some US bills would be a hardest one but it does not substantiate the marriage.
All the other stuff? Trivial to fake. These days, even a lewd sex picture can be done without the act.
The best one is pregnancy validated as one of the parents'. Kind of expensive.
See where this is going? If they don't want to let you stay forever, they will find an excuse.
An American can get married to a foreign national, and the marriage will be recognized for tax purposes.
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Yes, you've listed all the various ways that a vindictive USCIS can screw someone applying for a spousal Visa. That's very clever and all, but is irrelevant for the vast majority of applicants.
And the ones for whom it is relevant are going to benefit more from speaking to an immigration lawyer, than running over what-if-wargames in their head.
People adjust (or gain) status all the time while they are here already in US on some other visa. Having a temporary visa is has no good or bad effect on getting green card. Its similar (easy or difficult) in other countries as it is in US, its not "easy" in other country(ies) to fake address if it is not easy in USA.
Pregnancy (removed from all facts, sole pregnancy) is never on its own a proof of bonafide relationship. Who is the bio father? The whole collection of proofs when seen as collective, tells the picture & intent.
USCIS & agencies has to follow a manual & policies & procedure (much of it is published on USCIS's website), & 99% of the time the officer can not intentionally bring a personal bias (exceptions apply). There are millions of cases getting passed, & a single USCIS employee does not decide a single case. Like any other big organisation, everybody is doing apart of process. & they have managers, & managers above them. Even USCIS itself is not above law, people routinely sue USCIS in federal courts to challenge their decisions (or lack of decisions).
Not everyone has all of these things as evidence to a sufficient extent, but most people will be able to provide enough of them to convince immigration. If they can't, if they are lucky, they may get a request for more evidence, instead of an outright rejection.
IANAL.