Larry Ellison is seriously underestimated as a database leader. I worked at Sybase. Oracle beat us fair and square. The Oracle DBMS team is outstanding.
Not really--MS SQL Server was Windows only and took a while to grow. Oracle ran everywhere and was simply a better database by the mid-90s. (Previously Sybase was quite far ahead.) Oracle had row-level locking and MVCC at a time when Sybase was still stuck with a cumbersome page locking model. Oracle was also more reliable at least in my experience. I used to hit page corruption pretty regularly on Sybase but almost never on Oracle.
Disclaimer: I worked at Sybase. It was an outstanding company in the early days.