The real concern for meaningful space debris issues is in the regions where decay requires 100+ of years.
The articles mentions the ASAT because that's what they used to study orbital behavior and decay.
Also generally, Space.com is universally agree to be the single worst 'space news' page known. I would never use it as a source for anything.
waste -> vast
But for anyone who's not 100% comfortable with English, "the vast majority" is not simply a case of a descriptive adjective modifying the noun "majority," but it's actually a common phrase. People don't say "the big majority" or "the large majority," it's specifically "the vast majority."
If you wanted to use a different adjective, you could say "a large majority," and that would mean something like "most but not all and the 'but not all' is kind of significant" where as "the vast majority" means "nearly all of them, and the 'not all' is insignificant."
The real danger is space junk that's at much higher altitudes. OneWeb and Telesat Lightspeed (in planning) operate at 1000+ km, where space junk will take 1000+ years to deorbit on its own. And OneWeb has already had a satellite failure where it can't deorbit the satellite.
Compared to that, anti-satellite missile bust a satellite into pieces and carry indeed the danger of creating a Kessler syndrome. In case these would be used on a large scale, WW III would be imminent anyways. Apart from that, missiles are too expensive to knock out Starlink satellites, and the latter are comparatively easy to replace.
Is that right? Scientific American seemed to think it could be a problem in 2019[1]. Space.com says Starlink satellites orbit at an altitude of about 342 miles (550 kilometers)[2]. And the Wikipedia article on Kessler Syndrome[3] (which is a chain reaction of satellite debris) mentions an incident at 555km that was problematic:
"In 1985, the first anti-satellite (ASAT) missile was used in the destruction of a satellite. The American 1985 ASM-135 ASAT test was carried out, in which the Solwind P78-1 satellite flying at an altitude of 555 kilometres was struck by the 14-kilogram payload at a velocity of 24,000 kilometres per hour (15,000 mph; 6.7 km/s). When NASA learned of U.S. Air Force plans for the Solwind ASAT test, they modeled the effects of the test and determined that debris produced by the collision would still be in orbit late into the 1990s. It would force NASA to enhance debris shielding for its planned space station."
[1] https://www.scientificamerican.com/article/spacexs-starlink-...
[2] https://www.space.com/spacex-starlink-satellites.html
[3] https://en.wikipedia.org/wiki/Kessler_syndrome