This is how you have to look at things: https://www.swrve.com/images/uploads/whitepapers/swrve-monetization-report-2016.pdf
There are players who always spend on everything. They make the less than 0.5% who are responsible for ~50% of the revenue. This group is subject to retention measures and needs get fed with new stuff frequently. As long as you can deliver you are safe.
As for Revan, there were a lot players who spend small amounts regularly, but a considerable amount for the first time. Plus there are people who might spend now on Bastila Fallen to make up for not having spent on Revan. They are a larger group than the first but contribute far less to total revenue. Both of these groups are to be converted to players who spend large amounts regularly. And some of them will convert.
It´s not about how long a meta should prevail. It´s about the perfect timing for new stuff and the likelihood that your target players do spend again.