The phrase "less credibility" means that someone or something is not seen as trustworthy or reliable, making it hard for others to believe or rely on them. Full definition
But you have no scientific research to support your position on your blog and breastfeeding your boy until 4 years old lends to even less credibility to be honest. (thebadassbreastfeeder.com)
We thought it was perhaps because business has less credibility now, or such attacks were priced in. (theguardian.com)
But their push has less and less credibility as scores go up and students see more and more success. (insidesources.com)