What I wanted to say is to take a lot of care to not define your self by your weaknesses. If you have several startups with other people you are already awesome.
Then consider that there is nothing bad with your speech. Instead there is something bad with the expectations. You are a founder so you set the expectations. Setting meetings with agenda, not improvise decisions, maybe your focus should be more in expectation management for meetings than improving your speech.
And last. Consider if there is really a fit. I probably will love working with you. Other people might not.
Look also for a fit. I will like to work with you. I like to have a meeting, reflect, and come to conclusions after several sort sessions. Other people (not looking at sales), tend to prefer (in my short experience) meetings without agendas and fast decision making. The CEO should bring versatility to the approach.
Long live to slow thinkers! https://sive.rs/slow
Joining Toastmasters is a good option. They focus on helping people improve in speaking in a variety of settings. Speaking well takes time, effort and practice. I doubt there are any easy shortcuts.