Standard oil reduces the cost of oil, delighted customers, and had already a massive decline in market share by the time the antitrust stuff happened. It was driven by people who couldn't compete.
It also didn't hurt Rockefeller in the slightest. To the contrary, he actually became far wealthier post-breakup, possibly because all former business units became more efficient in the light of open competition.
Many of them live on today, such as Texaco, Chevron, and Mobil.
https://historyincharts.com/the-legacy-of-the-breakup-of-sta...
https://www.britannica.com/topic/Standard-Oil
In general, trustbusting almost never actually works as planned, but it always seems like a good idea -- a desperate solution, perhaps the only possible solution -- at the time.
The only thing that tends to work is upstart competition driven by new technology that blindsides the older company.
When it comes to a monopolist, the one thing that we can say historically is that, "This too shall pass."
Then it sounds like it did work in the eyes of the people who wanted more efficient corporations (and thus potential savings to be passed down to them).