The biggest problem with Varus is that he has to stand in place for a couple hours before firing one arrow. Everyone else instantly throws their axe or shoots their gun, but Varus has to pump his bow, like, 3 times before actually shooting. It really takes away whatever range advantage he might have in lane because the opponent will have plenty of time to react and trade, from which I don't see Varus coming out on top even if he has his passive up. If he loses trades and has a poor AA then he'll be easy to zone out from CS and it will take him longer to get to late game.
Late-game he can be strong, but that's the nature of AD carries. They are supposed to be strong late-game, but compared to others he falls under. He has no form of escape (which is why I think he should get a move speed boost along with attack speed on his passive) so he has very little room for mistakes in positioning compared to... everyone. KogMaw and Caitlyn has range, Ashe has range and slow, everyone else has a blink. His attack animation gets in the way here too, making him less potent than he should be and making him even more vulnerable to positioning. Blight is cool, but a failed concept imo. It encourages waiting before you use your spells, so you have to debate between dealing as much damage as possible or using your cc as actual cc and not blight fodder which you'll often be wont to do because that's your only tool of survival without a team designed to peel for you which leads to the question: Why would you make a team around an AD carry when everyone else does that carry's job better in any situation? Varus is weak in lane and weak late-game and needs a team. That's a lot of weaknesses.
I believe Draven competes with the trinity because he hits just as hard as they do and he has a built in ghost that refreshes from Spinning Blades. His harass is strong with his ability to Blood Rush in -> Q -> Blood Rush out (if necessary) and he can capitalize on aggressive play very well with his high damage and a low cd cc. He also scales hard since his bonus Q damage can crit and his ult offers upfront aoe damage which is what I think this meta is all about - Upfront damage (and bullcrap cc that ignores tenacity).