Disclaimer: The following suggestion only works if you only READ from their DB. Can you roll your own DB that matches theirs schema-wise for the tables you nee

Disclaimer: The following suggestion only works if you only READ from their DB. Can you roll your own DB that matches theirs schema-wise for the tables you need, but doesn’t suck in terms of availability? If you can get that set up, then in places where there are writes to their DB that you care about, also write to yours. Do a one-shot migration to copy data you care about after you land your change to double write. Then, modify your app to read from your DB and ignore theirs. Finally, once everything has been running smoothly for a while, collect data showing your system is better than theirs, get them fired, and become the new DBA for your company :)