That's just sci-fi though. Sure they aren't possible with our current understanding of physics or the universe however they are explained through scientific means in the fictional universe. They could maybe be considered magic in our current universe however it is still technology and based on scientific theories (albeit fictional science) and hence science fiction, not magic. If you somehow went back in time and showed someone a plane or a phone they'd believe it was magic.
Also you claim FTL isn't possible, it's possible wormholes allow for travel over great distances faster than light. Or there could be another undiscovered aspect of physics which allows for it which is just what Halo is describing. That's the point of science fiction. It's fiction, however it's rooted in scientific theory.
Bolded explains how i think about it. Do note that i call only things that are pretty much impossible magic, speculative things that are
still grounded to reality, like new materials or odd life doesn't count (but a material that, say, blocks all radiation but isn't dense is really magic, pretty sure the only way to cut down radiation is density, correct me if i'm wrong though).
Also magic is not necessarily a problem, just when a thing is introduced but its consequences are not thought about. If i see as a reader/player/watcher/whatever a possible solution that goes unused in-universe, i'm going to be bothered by this.
And i do keep saying it is not magic in-Haloverse.
And FTL is not possible due to causality problems. Undiscovered aspects of physics are still limited by it (new theories must still explain old experiments and whatever else).
You can't really dodge the time travel issue... Unless time travel is actually possible. Then causality would not what we thought it was, of course. But that's another matter. (Also ignoring moving between universes, which has its own set of issues.)
Wormholes don't actually dodge the causality issue, you can make a time machine them quite easily. You could also make a kind of a perpetual motion machine with them (free relativistic weapons for everyone!!!).
(Interestingly Greg Bear did try to fix this issue in the Forerunner trilogy, by slipspace causal reconciliation, or some such. Presumably some sort chronology protection system, that prevents action if it would cause paradoxes. Those books had a lot of small details, which was nice.)
EDIT also not going to say any more about this today.
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Speaking of time travel, did they canonize that Halo 2 ARG? And that one Spartan from Dead or Alive games? Both cases had time travel if i recall correctly.
EDIT Wait, what, Breaking Benjamin song is gone from Halo 2? FUCK!