However, that being said, the drop of interest paid on accounts that power up Steem also lowers the incentive to hold Steem power at all.

There is actually more incentive to power up after the changes because the more liquid steem the more "interest" for people who are powered up.
The 3 months withdraw period means there will be a lot more steem that are not powered up and so the ones that stay powered up will receive more interest.