Reason of poor performance of ANSI joins in Oracle 9i
Well, after a long time with no answers. I've done some testing.

I ran the same query in 10g and 11g and both versions, the one with ANSI joins and the ones with the WHERE joins run in less than 1 second.

As problems exists only in 9i, the same version the support for ANSI joins where introduced I assume it's a bug in 9i that could or could have not be solved in a patch.

Gladly as I mentioned, from 10g onwards both flavors of joins perform well.