I've found Claude to be very useful when writing on the EA Forum. However, certain prompting and other techniques can help a lot.
The main use case I'm personally interested in is writing and interacting with content on the EA Forum / LessWrong and similar, but I'm sure there are other use cases that would be relevant to this community.
Would a potential cure to the sycophancy be to reverse the framing to Claude, so that it perceives that you are your opponent and you are looking for flaws with the comment? I realize that this would not get quite what you are looking for, but getting strong arguments for the other side could be helpful.