To expound on the above, there are two kinds of "loophole" in law. One is an aspect of the regulation which was not anticipated by the lawmakers, or is an explicit use of the definitions used in the regulation. The other kind is more accurately called a "leave out" where some special interest group gets the definitions written to explicitly exclude their activity from the regulation.
That latter is more seen in tax code, but exists in some gun regulations, like if carry is restricted in, say, amusement parks, which are then described by very specific square footage size. Rare, but occurs.
Loophole most often has a pejorative connotation, so, yes, it is wise to avoid using it.
During the federal AWB, using a "thumbhole" stock was not exploiting a loophole, it was exercising the definition of the law to one's advantage. It was a "loophole" to the antis, who saw it as scofflawry, but was perfectly legal given the intent expressed in the definitions of the law.
And, we always want to look at the definitions of the law, and not our impressions, interpretations, or imaginings of it. Which is doubly true here in Legal.