Chris Jericho and Kane, easily. I know they won world titles, but they spent 99.9% of their careers during that time in the midcard. Being a Main Eventer or a Mid-Carder is a general summation of whatever your positioning on the card is.
The New Age Outlaws, Ken Shamrock, and Val Venis all deserve a shout out as well. The Outlaws were arguably the most charismatic and entertaining tag team of all time (well, actually Road Dogg was the charismatic one while Billy was the 'workhorse' of the duo for lack of a better term, but still), Shamrock was intense as fuck and with the right push could have probably been a world champion in almost any other era, and Val's porn star gimmick and sexual jokes before every match were witty and amusing, too.