interestung that the premium over mysql seems to be 0 in the "bring your own license" mode, and less than 50% when getting the license with the service.
So a single "large" resrved instance would only cost 400 dollars more a year.
The "with license" service only includes Oracle "Standard Edition One" which lacks lots of features. It doesn't have partitioned indexing or RAC for example -- among other missing features.
Why should it be any different? Applying patches is likely the same effort for Oracle as for MySQL. If they hadn't done this, some startup would have tried to feed off the arbitrage.