I am not a particularly big Jeff Hardy fan, but I think you are underselling him. He was massively, massively over in 2007 and 2008. I believe he was outselling Cena in merchandise, he was spiking house show attendance and also spiked ratings. He connected. Thing is, later that year, Triple H beat him in 3 matches on back-to-back PPVs so he was never allowed to reach the tippy top level. They might have undercut him cuz they never expected him to get over so they had to cut him down to size, which is emblematic of everything wrong with WWE today, or because they didn't trust him to stay out of trouble, in which case they were absolutely correct, cuz hindsight proved them right.