Google Adsense Custom Ad Sizes , google ad

The Google Adsense team had contacted us a few weeks back and asked to remove the custom js ad units which we were running on our network of blogs. These were the ads which we were allowed to run on a few selected number of blogs depending on the traffic and the demographics. We have been running custom ad sizes on our blogs which generally were the single ad units but with different fonts and sizes and which would not totally look like a advertisement. All of the sudden someone from Google had contacted us with the following email 

Dear Publisher,
We are currently in the process of migrating publishers from Custom JavaScript formats to standard iframes. By moving publishers over, we are able to offer more features, innovating faster and more efficiently. As such your Custom JavaScript publisher features will be turned off on 6th December 2013.

We apologize for any inconvenience this may have caused.

For technical questions and troubleshooting, please send an email to our AdSense support team while logged into your Google account.
Best regards,

We were quite confused and when we got in touch with them, we were told that the results from the custom ad units were not par with the default ad units and hence Google is taking a decision to stop serving ads through this option. This was a kind of shock because we have had done a few tests and found that the custom ad units were generally giving us better results, but now are told that its actually bad for the publishers and hence we should switch back to the default ad units by Dec 6th