If you write about time travel you have to deal with einsteins theories - you are correct, it's a theoretical side effect of this theory, but whether it's flawed or not... i for one wouldn't dare to invalidate einstein so easily, bigger men than you and me tried this and failed.
I don't get why you think the gravity issue is a non-sequitur: time, mass and speed do behave like einsteins theories predict it - if you say it is flawed, fine, but then you have to come up with some facts, and better yet, with a corrected, better theory to replace the one you're trying to invalidate!
The issue of gravity affecting time is a bit of either (un)intentional misdirection, or a simple mistake by the scientists. I'll explain.
Take the simple experiment of 2 synchronized atomic clocks and one gets a jet ride. After a while the clock in the jet (depending on the east/west direction of travel) shows either a faster or slower time than the ground-based clock.
The usual explanation is that time changed. But the Reality is simpler. Time didn't change, the tool to measure it did.
Atomic clocks base their measurement on known spin cycles of specific atoms (the details don't matter, you get the point.) But when forces (such as gravity) affect the spin rates of those atoms, it affects the clock.
Imagine a wind-up watch whose spring is almost unwound. The watch runs slow, but that doesn't alter time. Same with using measuring tape made of rubber. A 4-foot item can shrink to 3-feet when the tape is stretched right. A stupid thing to do of course, but you get the idea. I've outlined this issue before in
this post.
And please, i said "travelling back in time", but this applies to (sub)atomic particles (if at all), you took this the "time travel way and made it "people travelling back in time" - this was not what i said. I also didn't say that this is possible (if anything, i believe only info can somewhat "jump back", but not mass).
To me, talking of time travel whether mentioning a tachyon or a ship of people are the same thing. One is simply bigger and much more difficult. But ok, we can drop the big things.
Einstein-Rosen bridges work the same way - you arrive instantly, but you didn't move faster than light - nonetheless you made a "time travel" in the form i outlined above.
Ahh, the wormhole. I read Stephen Hawkings "A Brief History of Time" back when I was a teenager (Still have two copies of it on my bookshelf) I never was able to believe that wormholes were real.
And around 2007, Hawking came out an admitted he was wrong about that. IIRC, he was specifically talking about using black holes as wormholes and "coming out the other end", which is what he admitted wouldn't work.
However, back on the specific topic, yes, under certain conditions, certain items can travel FTL.
Edit:
My mistake, the Hawking retraction in 2004 was about black holes swallowing and never regurgitating. (
News source here)
