You could of course doing this without someone else's glasses on, whatever the colour may be.
Personally, I am not interested in figuring out who to "listen to", but knock yourself out ..
I look at what MFs of Bradley's caliber make in world football, and go from there. His value has declined here, he is 2 years older, and has been poor for USMNT.
There is no transfer value in Bradley given his salary. Same as there was no transfer value in Defoe (although that got cleverly masked by taking back another overpaid player with no transfer value)