Unless you count btc38, yunbi, and bter as "holders" because they hold people's BTS for them, then devs collectively are definitely one of, if not the top whales. Personally I am not counting the exchanges as if they were one entity, as they have obligations to many people.
If we look at how voting happens, the biggest vote chunk that ever gets added is around a 5% stake. Either thats the devs, or there is another whale of that size, or both.
If the devs are ~5% and that is the top holder, then decreasing that by .4% means more decentralization of BTS stake.