That’s not to say there couldn’t be some allophone difference. It might help if you tell us your native language just to be clear, because that can impact what people hear.
I live in Scotland. I’m not sure if that would have much of an impact.
Listening to an actual example of a づ, 手作り, I can hear a distinction between the proper づ sound and the sound I’m mis-hearing in 放つ. So it’s just me mishearing, I guess.
The づ in 手作り sounds like ず to me, as I expect. The つ in 保つ and 放つ sound the same to me, like つ. There might be a slight z quality to Kyoko’s version for 放つ, but not all the way づ/ず, sinceI still clearly hear the t as well.