I don't know where you heard about a creativity crisis but in the early 90's there was indeed a huge crisis which weakened the anime industry for a few years, along with a lot of other industries: an economic crisis.
In the world, we more-or-less refer to this crisis as the "Early 90's recession". In a few words, it was a massive and worldwide economic crisis which started after the market crash called the "Black Monday" (Monday, October 19, 1987 to be exact).
In Japan, they specifically call this period the "Lost Decade" (sounds like an anime event, right?). I don't think economics courses interest you here so I'll just show you how hard Japanese growth crashed.
So, to summarize, Japan had huge economic troubles during that time, so it's normal that both anime quality and quantity were seriously harmed.
As this article explains, even if the number of television anime gradually recovered, because of these economic issues the whole anime industry has never recovered the greatness of the 80s.
A slump in advertising revenue, a lower birthrate and the popularity of others forms of entertainment like video games and cell phones have led to sluggish prime time ratings and a decline in the number of anime since the peak in 2006.
I add that the death of Osamu Tezuka (Astro Boy) during this period could have contributed to that "creativity crisis" you were talking about.
To go further :
- Osamu Tezuka
- Black Monday
- Lost Decade
- Japan's GDP
- The struggle of the anime industry