Can I use one word to mean "what is even worse"?
You can introduce the mention of the additional deficit simply with the word worse:
Worse, it creates instability issues.
Or:
{Even worse / Worse still}, it creates instability issues.
You can introduce the mention of the additional deficit simply with the word worse:
Worse, it creates instability issues.
Or:
{Even worse / Worse still}, it creates instability issues.