Theres is 2 different problems here. One is that too many people have started to take the frt table as law, which it isn't. The mere fact that it isn't public disqualify it as being part of any law, bylaws, or anything more official than an apple pie recipe. Fighting anything in or about the FRT can be done in courts, which "only" takes money, and in most cases these are fight that are fought on a battleground ruled by reason and the rule of law.
The problem is the political reaction to everything and anything. Even a win in a court of law can easily be of very short term, since politicians can change the law at almost any time. The best example is the 25 rounds 10-22 magazine: the rcmp has declared them illegal, and they obviously are not, given the current law. If any case ever makes it in front of a judge, the magazines will be deemed legal, obviously. All it takes is money in this case. But it's what happens next that might very well suck: politicians changing the law to make butler creek magazines illegal, and maybe a bunch of other ones at the same time. A win in a court of justice could quickly turn out into a political loss if the parliament decides, for example, to restrict the capacity of every rimfire magazine to 10 rounds, regardless of anything, just to "plug a loophole".
So if we go back to that particular AR15 that's prohibited, which kinda sucks, the problem isn't really that this one is prohibited, the problem is twofold:
1-A law that was meant to ban full automatic firearm is used to ban a semi-automatic firearm;
2-Should the court decide to reverse that particular ban on the ground that the XM177E2 is a semi-automatic and isn't "easily converted to full automatic", parliament could act in a reactionnary manner and simply prohib every AR15 in the country by name.
Although the first problem could be solved in a court of law, the second one is very political. The first problem can be solved by a single person in a courtroom, no matter if the rest of the country disagrees. The second one, not so much.
So although we can collectively fight stupidity in courtrooms and win every single time, at some point a political problem will arise and the whole firearm act will have to be re-written from scratch. A lot of effort should be made by gun owners and businesses to make sure than when this time comes, the right people are sitting in ottawa, because otherwise we could find ourselves with nothing but airsoft and paintballs.