There is quiet a misunderstanding of how Riven works which leads to more ignorance.
Yes, she has 4 dashes which are her engage or disengage. But after using her 4 dashes she is a sitting duck without anything. New runes has messed her early game even more, like she wasn't messed up already by playing against high base damage tanks. She is starting with 0 cdr, so after using her Q you have a 10 second cooldown window to do what you want, after using her W you have 10s cooldown window, after she uses her E you have 10s cooldown window.
This still doesn't explain it? Alright, moving on.
With fervor out of the game, she is alone on top against mostly high base damage tanks like Poppy, Maokai etc. These tanks can out-trade you easily. You! Not you out-trading them as bruiser,fighter,assassin but tanks. You don't have damage to deal with them and most of tanks are counters naturally to Riven who just get Tabis and you are done for.
Poppy has he W to counter your engages.
Malphite has his E to lower your attacks speed.
Maokai has his Q as displacement for your engages and W for your all ins.
Olaf with lvl 6 which makes him cc free, makes you irrelevant .
ChoGath has his Q to counter your engages and W to silence your all ins.
Ornn has his W as cc free and free shield.
Shen has his W to counter all your auto attacks.
Garen with a low cooldown Q silence.
Urgot with knockbacks for your all ins.
Nautilus with Q,AA,R stun.
The list goes on. This tanks are natural counters to Riven and with Ninja Tabis rush, they are without a help of your jungler unkillable (Unless they mess it up). Junglers tend to have mixed feelings about Riven, sometimes they would know the potential of Riven and would gank her to help her, while others tend to forget she exists on top, leaving her on a mercy of a jungler and a toplaner. This is also fine, since a jungler will most likely pay attention to other lanes and hopefully carry there. But this is not the case. Junglers will see you getting ganked over and over, but wouldn't do a thing and would call you out later on for dying while he forces camps on mid or bot that has lost way before Riven. It's basically a fact that even if you are playing adc Soraka, you will get ganked over and over by your jungler, while Riven who can hard carry is forgotten. This is not a bash on junglers but rather a Riot not giving you anything for toplane.
How so?
Well, imaging you are Riven against a hard bully like Jayce? Right? A champion that will harass you and zone you from all your exp and gold. Now add a summoner changing rune to that which gives him if he wants ignite early to demolish you, to get even a bigger lead and later take tp to split push his way to your nexus. Compensation for this? There isn't any. You are just there to get your 3 cs out of 10 under your turret while Jayce AA you, until he gets items to dive you. Over and over.
Her winrate has 2 sides of answers. One is that it's preseason and there are some that are practicing her, while others that already play her, struggle to win. Her build has pushed her more into the cave. The damage taken out from BC a starting item has disabled her to do anything until she completes 3 items.
How so? Well, now that the damage is taken out, she is forced to get warhammer to compensate for the lost damage, because if you have only BC you don't have damage but armor shread and if you just have warhammer you only have damage without armor shread. The next item would have to be a life steal so she can fight an already Omen,Thornmail tank and boots in the end. Sometimes this isn't enough, 3 items, because it depends on how well your enemy top is doing. If he plays it correctly and tps with success, you are going for a long waiting game until you have full item set.
When it comes to bullies;
Pantheon has a passive to neutralize your AA.
Jayce will zone you out since he has 2 forms to deal with you and after using 1 form the other one has free abilities to take all of your hp.
Kennen has his long range AA with 2 stuns and high damage.
Swain is wasting no mana with his Q,W,E which helps him get to 6 easily to just abuse you even more.
Akali has an insane damage from lvl1 and onward.
Lissandra from her passive gets a free ability and has a low cd on her W to stop your engage and R to stop your engage or to ult herself to get some hp back.
Teemo tank with a blind is a disgrace to this game.
Heimer keeps pushing you with his turrets and places turrets just under the turret range.
Quinn,Vayne on top is not even worth mentioning. Don't know what's worse.
And the list goes on.
So, after you look at these both lists how can you say she is a bully. If you pick someone from this list, it's definitely you and not Riven. Cause i just explained to you. These lists are too long for toplane. It shouldn't be like that. She is a melee champion which gets all her damage from AA. How so? Well her Q deals little damage and has a long cd while her W is similar. The damage she has comes from her passive which gives her empowered Auto Attack after using an ability. All of this is taken away when Ninja Tabis got a 12% AA damage reduction buff.
She is currently sitting at whooping 48% winrate. She is a high skill cap champion that is hard to master, not learn. If you want to master her it will take hundreds of games but if you want to learn her it's straight forward. Do me a favor and dash in to your enemy to show your 'dominance and bullying power' use all of your 4 dashes as you say, cause she is such a mobility champion. And after you do and he is still alive (which he will be with 70% of hp) you are dead because the next ability will be available in 10s.