Not true, Riak was completely, 100% correct with siblings enabled, which is Totally Expected behavior for a standard Dynamo-style system.
The criticism is that last-write-wins is the default, and that's a fair criticism--that's not an honest default for a robust eventually consistent system like Riak. My guess is they default to LWW to ease onboarding of new users. Everyone is worried about rivaling MongoDB's out-of-the-box experience so you don't scare people away...
TBH, though, if you're using a distributed, eventually consistent storage system without understanding the consequences, you're probably using the wrong tool.
The criticism is that last-write-wins is the default, and that's a fair criticism--that's not an honest default for a robust eventually consistent system like Riak. My guess is they default to LWW to ease onboarding of new users. Everyone is worried about rivaling MongoDB's out-of-the-box experience so you don't scare people away...
TBH, though, if you're using a distributed, eventually consistent storage system without understanding the consequences, you're probably using the wrong tool.