90% of all performance issues are I/O related. If you have just 1 year of transactions in your database files, your performance issues are minor compared to having 12 years of transactions. The worst performing applications can perform well if you focus on database tuning.

Our Query Optimizer identifies SQL and query performance issues that can be resolved without having access to source code.

Our Disk Navigator finds neglected transaction and history files that need more attention from purging, archiving and indexing standpoints.

The Journal Optimizer finds mistakes that were made on your system in regard to security auditing and transaction journaling.

The Spool Navigator can identify changes that you should make to your job descriptions so that unnecessary spool file generation isn't impacting your system negatively.

The Application Optimizer does typically find necessary code changes. Helping your software vendor find and fix their code is sometimes an option. This is just one of the 7 tools in the tool-set though. You get them all. Do what you can in your environment. If code changes are not an option, just don't use this one tool.