I think you are referring to the Webex Meetings Desktop app to Webex App upgrade, aren't you?
The Webex App just bundles all workloads (Meetings, Messaging, Calling) into one application. It allows you to prepare meetings in advance via spaces or just a quick chat with a collegue. You may schedule dedicated meetings as well, no need to create a space for them -- but then you will not have those space features, for sure.
As all Webex sites will be upgraded, all users may use the Webex app soon, so no worries about that. And for sure, users may also join via browser. Joining a meeting with the Webex app does not require an account, you can also join a meeting without.
Scheduling via Outlook will be possible as well (my favorite is the hybdrid calendar integration). There is an web add in for Outlook as well (productivity tools will be discontinued). But you may also schedule your meetings directly from within the app or via your meeting site, for sure.
