That's one of those things that only SOUNDS easy. In actual practice it probably wouldn't be.NuTrek screws with this concept to such a degree for the sake of plot contrivance that you have to give up trying to explain it. If it is possible to transport a living being over several light years safely onto a ship at warp or another solar system, it would be child's play to cripple or destroy a ship as long as you have detected it on your sensors. Just beam away chunks of it before it can react or beam out as many life forms as you can detect and keep your new shiny ship for yourself.
Transwarp beaming has a lot of potential as a sabotage/assassination weapon, used on a very small scale, under ideal circumstances with a lot of intelligence overhead and premeditation. Somewhere in the Abramsverse, if you dig deep enough you will probably find at least one instance of Section 31 or the Tal Shiar using a transwarp beaming device to snuff out some uppity Klingon general and make it look like an accident. It's an interesting kind of trick, but it's hardly a silver bullet.
I'm not convinced they don't. Starships run with navigational deflectors as standard practice, and space is full of cosmic rays and charged particles that are difficult to shield against effectively.Of course, this would lead to an arms race whereby all ships have shields up all of the time
It seems to me that the ubiquity of basic navigational shielding is one of the reasons transporters prefer to beam people from one transporter device to another; that's just easier and safer with all other things interfering. Sophisticated Starfleet transporters probably have some kind of ECCM devices that can penetrate low-level shielding nine times out of ten, but high-level shielding is either too hard to penetrate or too dangerous to try.
Which is another thing I liked about the Abramsverse transporters. They depict the beaming process as a lot less "push the energize button and there he is" and a lot more "Have to keep the transporter beam perfectly focussed on that target for like eight seconds or nothing much will happen." Apparently all the various tricks for increasing transporter's efficacy -- including transwarp beaming -- are really just complicated mathematical algorithms that make targeting easier.
First of all, "internal sensors" in this context basically means surveillance cameras and intrusion alarms on hatches and consoles. Narada is a mining vessel, so its internal security is probably geared around preventing theft and keeping the crew from accessing materials without authorization. OTOH, Starfleet's "internal sensors" aren't much better, so Narada's security seems pretty standard (if you think about this, modern Naval vessels operate more or less the same way; security isn't monitoring the ship's internal spaces, just its equipment).
Second of all, again, Narada is a mining ship; it's crewed by a bunch of Romulan factory workers who are NOT, in fact, ninjas. There are probably two or three people on the entire ship who are actually trained to operate a transporter system, and they only have civilian training; the rest of the crew probably knows as much about transporter operations as YOU do.
This assumes, of course, that the Narada actually HAS a working transporter system. This isn't known for sure.
I agree that beaming into a ship at warp should be crazy hard but then if all you are beaming is a chemical weapon, you don't have to be anywhere near as accurate as with a living being. Beaming onto a ship that isn't at warp should be much easier, especially with non-living matter so then it just becomes about distance. Ships can't automatically detect each other at great distances as transponders are encrypted and space is so big but with the kind of distances in NuTrek it's not a risk any ship could afford to take.
If navigational deflectors blocked transporters as standard then that would simplify things. Although they've never mentioned dropping navigational shields to beam in or out that I recall.
What I dislike about the Abramverse transporters is the inconistency. It takes ages to lock on when a woman is doomed but a second when Kirk wants to look cool. Quantum scanners should work instantaneously or what use are they? We're moving on the atomic level way faster than during an earthquake on a spinning piece of rock. It's the interruption in the confinement beam that should be the danger once transport has started and that's where I have difficulty with NuTrek. How much energy does it take to send a confinement beam 20 light years through subspace? They need subspace relays for communication signals but not for entire people? It's inconsistent.