You could make an argument that Berkshire Hathaway is the largest M&A firm ever. But it's not really private equity (though it's not really public, either).

Dell? Silver Lake played a big role in that IIRC.

In 2017, I joined a company that had been spun out of Ebay and bought by a PE firm. The firm invested a large amount of "growth capital" in the biz to transform the product from a software license to a cloud-based service. This transition not only increased our revenue exponentially but also gave us the ability to analyze data on how customers were using our product (prior to this, we had zero visibility into how customers used our on-prem product). Using this data, we were able to better serve our customers & partners and improve the overall experience of using the product. A few years later, we sold the company to a large company for a pretty penny (>$1B).

This is all definitely anecdata but, IMO, being backed by a PE firm forced us to focus on revenue (really EBITDA) alongside product growth. A mechanism that forced us to focus on the impacts of each product decision we made. I think this ultimately helped us keep a steady pulse on the market w/o chasing every shiny new trend that popped up.

Dynatrace is a monitoring solution and company that recently went public again after being initially taken private by a PE.

I believe their offering significantly improved during period.

(I was a Professional Services employee for a few years)

Limit that to KKR and you are going to see many "good" examples...

Hilton hotels in my opinion got much better after the takeover