Some examples of innovation that happened and were launched after the acquisition: buildpacks (at the time of acquisition Heroku was still Ruby only), Heroku Postgres launched forks/followers/dataclips all after the acquisition, review apps came several years after. Salesforce may have had an eventual hand in it, but there was still a lot of innovation happening due to the folks there in the near to mid-term after the acquisition for several years.
All that said, very excited for the new crop of players in the space. There are a number of companies trying to be a cheaper or more stable Heroku. Personally I'm excited about the ones that are taking their own unique approach. https://www.fly.io and https://www.railway.app are two that to me seem to bring their own perspective vs. just trying to recreate Heroku as a carbon copy clone. There are a number more in the jamstack space that have become staples such as Netlify and Vercel which are also doing great things.