The latter. 1999 / 2000 was the commercial peak of European epic trance - which, along with the entire "superclub" culture of the time crashed and burned badly around 2001, giving birth to darker styles like early 2000s progressive house (the exact same thing happened with Uk Garage around 2001, by the way, which gave birth to Grime). So I suppose you could compare Sandstorm with a popular record from the peak Disco era, for example, that capitalized on that style just before it all went south. Looking at it musically, Sandstorm definitely follows the formula of the style popular in commercial trance at the time: really DJ long intro with the drums appearing in 16 / 32 / 64 bar increments as expected, cymbal fills to mark transition points, plenty of snare rolls (one of the most 90s things there is, originally popularized by Hardfloor - Acperience), looong breakdown, supersaw-ish strings, offbeat donk bass. The most characteristic element is definitely the resonant lead but looking at say, late 90s hard trance I don't think it would be difficult to find similiar sounding tracks. Listening to it now, overall, the production and engineering is also very characteristic for the late 90s, being cleaner than most electronic music from the early 90s but not as clean as most music made in the DAW era starting from the early 2000s. The synths tones are all quite obviously from 90s digital synths (most popular at the time being the Nordlead and JP8000), which really dominated that era of trance.

What I find interesting about Sandstorm is that it's always been kind of a meme, maybe because of the iconic video? There are much more historically important smash-hit tracks from that style and era like System F - Out Of The Blue, Lost Tribe - Gamemaster, Gouryella - Gouryella or Rank 1 - Airwave but none of them have made quite the career that Sandstorm has.