Breaking up Microsoft absolutely helped their competitors, but not in the PC software market. There was a time when Windows tightly integrated Internet Explorer throughout the operating system to the point that using a different browser was a hassle (and would never be done by their general audience). Microsoft subverted and contorted as many industry standards as they felt like it as they attempted to turn the internet into their own walled garden right from the start. The antitrust rulings that were made undid the clamped down version of the internet that Microsoft was trying to build. I highly doubt consumers would have somehow been better off the last two decades if this ruling wasn't made.

the nature of capitalist competition means that in the long-term markets will consolidate.