I am going to speak up in defense of the Arya plot.
Yes, it was clumsy. But I don't think it was as egregious as folks are making it to be.
Arya laid a trap for the Waif. She knew they were coming and she laid a trap. That is why Needle was hidden away in that dark little hut of hers. Her plan was always to lure the Waif into the dark room, cut the lights, fight blind (as she was taught to do, unlike the Waif) and kill the Waif using the advantage of the imposed blindness to even the odds. It is a smart plan. The same people *****ing about it would ***** if Arya suddenly beat the Waif despite no indication that she has the skill level to do so.
The flaw in the plan comes from the Waif stabbing Arya. People have complained that Arya was behaving too carelessly, etc. Is it not possible that this was part of Arya's plan? She wanted the Waif to see her so she could lure her into the room to kill her. That is why she was gallivanting about, flaunting her money, etc. She was trying to lure the Waif into a trap.
Arya's key mistake is thinking that the Faceless Men would not attack her in public. It isn't a bad assumption to make. Think of Arya's experiences with the Faceless men so far. Everything had been cloaked in secrecy. When Jaquen killed Arya's targets at Harrenhal, he, by and large, made it appear to be an accident and in lieu of that used poison. It was subtle and stealthy. Similarly, when Jaquen assigned Arya to kill the thin man, he instructed her to poison him. When he ordered her to kill Lady Crane, he advised her to poison her wine. All of these tactics are subtle, stealthy and, in a medieval setting, could be attributed to natural causes or accidents. The only exception to these tactics is when he helped her escape Harrenhal, and that was done under coercion and Jaquen was not happy about it. Neither Arya nor the viewer had any reason to believe that the Faceless Men would attack a little girl in broad daylight and stab her. Arya assumed they would not go at her in such a manner. It was a mistake that caused her to be unguarded when the Waif attacked her, but it was one that her experiences with the Faceless Men led to her making. It isn't as inconsistent with logical thought as some may think. Arya simply assumed the Waif would wait until she was alone (in the hut) and then kill her.
So that leads us to Arya's wounds. She was stabbed twice, if memory serves. She seemed to be in pretty bad shape. But at least a day or two passed from being stabbed to her escape from the Waif. Further, one can assume that her behavior in Lady Crane's apartment, shortly before fleeing, was at least, in part, for the Waif's benefit. Crane's prolonged conversations with Arya about her being good at acting are hints to this. This was clumsily telegraphed to the audience, but it certainly sets the table.
Arya's entire flight from the Waif was a continuation of her earlier plan to lure the Waif into the hut and kill her. That is why Arya was leaving a trail for the Waif to follow. Further, their confrontation in the hut supports the notion that Arya was exaggerating her wounds/acting. She goes from whimpering on the ground, gasping for air, to calm, confident, and collected right before she slices the candle in half.
In essence, although poorly telegraphed, the wounds were never as debilitating as the Waif and the audience were led to believe. This was an intentional ploy on Arya's part, much like when Dany led the slave traders (and the audience) to believe she could not understand their insults that were spoken in Valyrian.
Arya's plan did not work perfectly. But it is all part of a logical progression and not as irrational as some are acting. This is not to defend the show. The writers and directors of the past few episodes failed as story tellers by not making all of this a bit more clear. They planted seeds but failed to cultivate the crops. Never the less, the groundwork is there.