The phrase "supposed experts" refers to people who are considered experts by others, but their expertise or knowledge may be questionable or not truly reliable. Full definition
I had taken the word of supposed experts and authorities. (nakedpastor.com)
But do not be chastened by supposed experts who insist there is only one way to enjoy a glass of whisky. (canadianbusiness.com)
Prior to the 2017 election, Corbynites were told by supposed experts like myself that, as Tony Blair had it, when a traditional left - wing party competes with a traditional right - wing party the traditional result will follow: defeat for the left. (theconversation.com)