In EA the SQL layer is not well written. Maybe they tried to "specify" some specialisation however they made wrong work.
They not use parametric sql, the parameters placeholders just replaced the value. Thats way Oracle must reparse every same sql hundreds, thousands (depends your size of model), and cannot use the statement cache.
I found a "bug" and slow execution. The problem is the classifier_id. In some table (eg. t_attribute, t_operation) the classifier_id is not number(10) but also varchar2(50 char). EA generate sql looks like "classifier_id = to_char(t_object.object_id)", thats way Oracle can't use index, because they need convert object_id and full table scan occurs.
I started a github project where gathering tips, what I found helpful to increase performance while Sparx fix EA with Oracle.
https://github.com/onlyonce/sparx_ea_oracle_tuning