I wrote up a brief description of Wing Chun's strengths and weaknesses here:
Defence against Wing Chun
The main gist of it is that Wing Chun's original design goal wasn't to make a well-rounded fighter. It was merely to train someone up in a very small amount of time to take advantage of the weaknesses of many kung-fu styles present at the time and location where Wing Chun was created.
Because they could very successfully exploit holes in the defenses of kung-fu styles around at the time, it didn't need to train people over a decade to master all aspects of fighting. It wasn't a "complete" system, and it didn't advertise itself as such.
If you look at videos on Youtube showing Wing Chun fighters vs. other styles, a pattern will emerge. They tend not to have good responses for styles such as Muay Thai, Boxing, BJJ, and other styles which were not around at the time and place where Wing Chun was created. In particular, they tend to be open to hook punches, high round house kicks, and of course grappling and ground-fighting.
In videos, the most "losing" strategy of Wing Chun is to wait for someone to come close and to try to "bridge" with them. They almost always get KO'd doing that. This is due to a very widespread misunderstanding, in my opinion and in the opinion of many Wing Chun people, that bridging and chi-sao is the way you "enter" in order to begin punching.
No, chi-sao is what you do when you can't punch. It's the last resort. Wing Chun people spend a ton of time on chi-sao exercises, but in fight videos, chi-sao is what tends to get Wing Chun people knocked out. They're just using it wrong.
Instead, what they need to be doing, as demonstrated time and time again in real fight videos, is to go on the hyper-offensive from the very beginning. That means getting right up close to their opponent and punching relentlessly. When their opponent backs up, they need to follow and keep on them, never giving their opponent a chance to get some distance.
They shouldn't wait to bridge and chi-sao nicely with their opponent, just like in their Wing Chun classes. That's a big misunderstanding and a bad habit they have. You do chi-sao when you don't have a chance to punch. Chi-sao is not a necessary step before making that punch.
When they charge forward and get right up into their opponent's face and keep following them with punches constantly coming, their opponents usually do not have a good answer for that. They'll continue to back up, but the wing chun guy keeps closing the gap. Hardly anyone has a good way to deal with someone who's in that short range and who is constantly punching them.
Many trained boxers know what to do in that situation, though. But most people are not ready for it. That's where Wing Chun can win and has demonstrated it can win somewhat reliably in all fight videos I've watched.
Another problem with Wing Chun people is that they don't often guard their heads like they should. That comes from fighting experience, which most Wing Chun people don't really have. You'll often see them in that Ip Man style stance with one arm way out there ready to bridge. That isn't a good guard. It leaves your head wide open. Any boxer would immediately destroy someone who does that, and that's precisely what you'll see in videos where Wing Chun is fighting someone from a boxing or MMA background. Again, this seems to be a very common misunderstanding of how to fight using Wing Chun.
So to answer the original question: Is trapping realistic? No, not very. It's often done wrong, at the wrong times for the wrong reasons. It can be used, but not generally as a primary way to get in on an opponent.
Can Wing Chun defend itself well against trained martial artists? Yes/no. Against many of the kung-fu styles it was originally intended to go against? Sure. Against styles like boxing, Muay Thai, and MMA? Not really. And part of that reason is that those styles do a hell of a lot more actual fighting than Wing Chun people do. Getting good at fighting means you need to fight, often. Or at the very least, you need to do a lot more MMA style sparring.
Hope that helps.
