Diamond did not take over the market as much as it was handed to them by Brunswick. Living in the past and not believing their equipment should get any better, they were ripe for the picking.
A shame really, but at least Diamond stepped up and is moving the game forward, with tournaments and sponsorship deals for certain events, etc.
So, you can dislike Diamond all you want, it's a free country, but you should dislike Brunswick even more for outsourcing their tables to far away lands, and for basically abandoning billiards in the US for the past few decades.
Yep, I own a Brunswick table, and my playing cue is a Brunswick Willie Hoppe Pro Model from 1940's. The table will be gone soon, replaced with a Diamond, the Brunswick cue I will keep