monami,
The source you cite is the opinion of the writer.
I think we need to put a little perspective on this. When the Amiga was first introduced in 1985, it could do things that nothing under $10,000 could do at the time. You would have to spend upwards of $20,000 to get the same functionality as the Amiga 1000. Because of this, the Amiga 1000 was a great success and made a huge impact on the computer industry. It was so advanced, comparisons to the Atari ST seemed absurd.
At the time of the release of the Amiga 500, CBM's general manager, Alfred Duncan, was quoted as saying, the Amiga 500 represents "a computer that retails for about half as much as the Amiga 1000 yet retains all of the performance capabilities - including advanced graphics and video, four-channel sound, built-in speech synthesis, and multi-tasking -- in a lower priced unit." With the exception of the ROM-resident kernel (the Amiga 1000 used a kickstart disk, but I believe ROM solutions were made available), it was, for all intents and purposes, an Amiga 1000 computer system stuffed into a Commodore 128 case. It had the exact same chipset and capabilities. Just as the Amiga 2000 was an Amiga 1000 with the ROM-resident kickstart and an open archetecture with seven internal slots.
Fact is, the Amiga outclassed everything in its day, including the Atari ST. Fact is, the Amiga 500 would have happened regardless of the existence of the Atari ST, as it follows the same evolutionary path as Commodore's 8 bits (Commodore PET > Vic 20 = Amiga 1000 > Amiga 500). Technology trickles down, and all-in-one computer designs were mainstaples of the home computer industry since the 1970's when we had the Apple II, Vic 20, and Atari 400.