In terms of making them mainstream, both Commodore and Tandy outsold Apple from the start, and the Commodore 64 went on to significantly outperform Apple's combined Apple II sales, despite being on the market a far fewer number of years.
Apple was not first, nor shipping anywhere near the greatest volume.
Old skool hackers will remember that the Atari ST and Commodore Amiga were massively superior both in price-performance and raw performance to contemporary Macs. Strange as it may sound today, Apple won on business savvy, emphatically not on technology.
"The Amiga was so far ahead of its time that almost nobody—including Commodore's marketing department—could fully articulate what it was all about. Today, it's obvious the Amiga was the first multimedia computer, but in those days it was derided as a game machine because few people grasped the importance of advanced graphics, sound, and video. Nine years later, vendors are still struggling to make systems that work like 1985 Amigas. --Byte Magazine, August 1994
Of course, the Amiga was originally conceived as a gaming box, but the initial price and inept marketing scuppered chances of real success.
I agree with you about the Amiga, it was a great machine that did not deserve to die.
Later Commodore got the Guiness honor of producing the most of a single model computer with the Commodore 64, no solid number but its above 12 million up to 17 million.
An interesting read is Brian Bagnall's book Commodore: A Company on the Edge, which has many accounts from Commodore's staff. One interesting tidbit, is Apples marketing at the time though they were third in sales (behind Radio Shack and Commodore) their ads touted "We are Number One!" of course there probably wasn't a mention of what they were number one of...
What Apple got for a time was a foothold on the Business market with VisiCalc, and also Apple Works (this is not the Mac GUI program Appleworks). They also got a solid foothold in the education market. Educational software was a very lucrative market for many companies during the 80s and early 90s.