You hit the nail on the head as to why people don't use Slack & Jitsi, and barely use Hangouts: it's the call quality, stupid. Zoom drops out less, video & audio quality is better, screen sharing works. It's as close to a "gets out of your way" piece of videoconferencing software as has ever existed.

Competitors, take note. Get the basics right - don't concern yourself with fluff - and customers will flock to you.