There are a lot of issues with the High Times Cannabis cup, at least the traditional Dutch one.
First big one is that because the cup is held in Europe, and requires submission of several ounces of buds, it can be a big uphill challenge for breeders/growers outside of Europe to enter. IE, nobody is going to smuggle a few ounces of bud from Colorado into Holland just to enter a contest! Also, contest entry criteria are a bit murky. . .its not the case that just anyone can enter. So traditionally, this contest has been limited to companies with a presence in Europe, mostly the Dutch-based commercial breeders. As a result, in practice, there are a lot of breeders who won't/can't participate and a lot of great stuff never even gets entered.
Of course there have been all sorts of issues with judging, including (IMO credible) past allegations of vote-buying and other abnormalities. For example, multiple cannabis cup winner Arjan Roskam of Greenhouse se-eds had two cup wins revoked ten years ago after being caught red-handed bribing judges. I think this issue has been addressed somewhat, but the locals in Holland still eye this cup suspiciously. Personally, I don't even know how its possible for anyone to really "judge" 20 strains of cannabis in a limited time period. Certainly you can judge their smells and appearance, but potency is problematic, because of issues of tolerance and cross-tolerance that occur with smoking a number of different things in succession. Recently, the HT contests have incorporated lab testing as a way to compare potency, and IMO that's good, though these things still don't tell the entire story.
Most important caveat here is that at best contests judge BUDS, not STRAINS.
In other words, if a strain is nute-sensitive, pest or disease prone, hermie prone, slow growing, low yielding, takes a really long time to flower, has tremendous pheno variation, or other issues, those things simply aren't going to be reflected in a contest evaluation. The judges never see the actual plants nor try to grow them; all they see are the submitted buds.
As a result, even if a contest winning strain does make legitimately outstanding buds, that doesn't necessarily mean its going to be a good (or even feasible) choice for YOUR particular garden. In contrast, the absolute BEST lines for any given grower may not have ever been entered into any contests, let alone won any.
Bottom line is, the contest has always been a promotional tool for the magazine, and that's probably its main purpose. Contests are nice social networking/business occasions for growers, coffeeshops and others in the industry. The HTCC has traditionally been the equivalent of the cannabis industry "trade show" and they're fun events. As ways to decide which strains are "the best"? Don't think so.