Without resources Vergil is mid tier at best. A character like Wesker can demolish Vergil 1v1 because it then becomes a footsie fight. If Vergil whiffs one st.H or Stinger he dies because most characters move so fast with ground dashes (if Vergil whiffs st.H/Stinger against Wesker he would be able to wave dash in, tea bag and then start his full combo). While Vergil can easily whiff punish other characters, he has to make a solid read or punish where as other characters can play more ham. This is why the percentage of resourceless Vergil wins are low and you can immediately tell a bad Vergil from a good one based on how they play in this situation.
That said he is rarely without meter, assists and XF in a match... all of which make him a huge threat. Vergil is a character who fully exploits the MVC3 engine all the way from the OSs, to the high damage, to the meter gain, XF, the buff stacking glitch, hit stop glitches, weird ass hit spheres, plink options, a hyper that crosses up randomly due to engine bug, loopable hyper due to properties on moves. About the only thing he doesn't exploit is TAC.