Well Vi in general doesn't seem to be doing too hot right now.
Her base stats are mostly on par with other toplaners, 2 things stand out though:
Armor is really low for a fighter, other fighters seem to have at least 4 armor more early.
She also still has 125 AA range. Quite a few melee toplaners these days have 175 now. It's a bit annoying do deal with in some circumstances but her E does help with that if used at the right time.
Vi toplane never felt like a champion I can use to duel with. You need to play her kinda like a Jayce, combo-ing the enemy and walking away, poking with E to keep them low.
Her kit feels to slow to fight reactively, between charge/ramp times and slow AA-animations its harder to trade when engaged on.
I see some of the recent games you played were against Irelia. Heh, not a very fair matchup I'd say, at least currently, she even has an extra 25 AA range to 175 which makes AA-trading very unfaviourable.
Ironically I use her against Ranged toplaners, like Gnar. They are pretty vulnerable to engages and she has the kit to catch them. Their range doesn't matter as much as those of melee champions since your E + shield pretty much outtrades their lower damage poke and weak base stats.
In conclusion though I think she needs 3 things improved to be more viable; her base armor, her AA range without E and perhaps her AA animations.