The thing is that Erza can lose. She's lost twice thus far in the series, versus Jose, and the 3/4 vs 1 against Oracion Seis. There's nothing wrong with her winning most of the time either, or winning with a single, unblocked sword strike. Erza is strong, and an unblocked sword strike will ruin most people's day. She was originally hyped as being one of the strongest wizards in Fairy Tail, one of three roughly equal people that only Gildarts and Makarov are above in strength, and hyped as possessing magical power comparable to a Wizard Saint. She's largely lived up to that hype, often requirings nerfing of some sort for her to have a good fight, and rarely encountering someone that's a close match for her.
The only problem is that her fights against opponents that are a roughly equal match for her are getting repetative. Her armor is insufficient and getting beaten by raw force, giving her opponent the upper hand, so she discards her armor to use all her power for offense and wins once she gets an opening. That's also far more boring than her analyzing her opponent's power and selecting an armor that mitigates it, or using her armors in a clever chain to gain the upper hand. Or her using one of her supposedly really strong armors like the Puragatory Armor and the Fairy Armor for more than jobbing or a single cataclysmic strike.
I don't think you understand exactly what I meant by losing. She will never be in a fight where she goes up against someone alone and loses because her opponent was just better than her. She will never be made to look weak is the thing. In both examples you quoted Mashima made sure to explain why she "lost". Whether she was poisoned or because she was weak after having taken the full force of the Jupiter Cannon. She will never lose like Gray did against his first encounter with Lyon or his recent match in the tournament. That is what I mean by losing. I mean here after taking all that damage from Kagura and those falling rocks she will still win against Miverna, and when a character reaches this point I just find them so dull. There is no suspense in anything they do anymore.
I do agree that her armors have become completely useless now though. All she does is use that sword, which adds to the problem.