As a founder you need to interact with customers, vendors, employees and investors. If those groups have trouble understanding your speech, then how could you not have a problem?
Really, this is not a debatable point among sensible people. The only part that is debatable is which accents are strong enough to pose a major problem.
Unfortunately most people don't seem to logically process what was said before deciding to argue. They just pattern match. If the pattern looks like something they argue with, then they argue. So people pattern match on his argument, see the word "accent", and argue on the basis of his comment being thinly veiled xenophobia. Which could not be farther from the truth!