1.I'd like to ask you a simple question: Why do you always say (human) NOT (huwoman) when talking about people in general? Are you implying that WOMEN are not among human beings?!!
2.Considering the above-mentioned point, we can understand the reason why the majority of the verbs and pronouns have been used for MEN not WOMEN. For instance let's take a look at the verse 21 of Surah Al-Rum as you cited in your question:
وَ مِنْ آياتِهِ أَنْ خَلَقَ لَكُمْ مِنْ أَنْفُسِكُمْ أَزْواجاً لِتَسْكُنُوا إِلَيْها وَ جَعَلَ بَيْنَكُمْ مَوَدَّةً وَ رَحْمَةً إِنَّ
في ذلِكَ لَآياتٍ لِقَوْمٍ يَتَفَكَّرُونَ
And of His signs is that He created for you mates from your own selves
that you may take comfort in them, and He ordained affection and mercy
between you. There are indeed signs in that for a people who reflect.
the word "لکم" means "for (all of) you weather you are men or women. That's why the correct translation of the word "ازواجا" is "mates" which include both husbands and wives. looking the word "زوج" up in an Arabic Dictionary, you can find that the definition is: both male and female when they are married. In verse 45 of Surah Al-Najm we also read:
وَ أَنَّهُ خَلَقَ الزَّوْجَيْنِ الذَّكَرَ وَ الْأُنْثى
and that it is He who created the mates, the male and the female
This question may come to the mind that " If the verse were talking about both men and women in general, it shouldn't have used the pronoun "ها" in the word "لها" which refers to "female" not "male". But the answer is simple because in Arabic "ازواج" is called "broken plural" and the pronouns referring to these nouns must be in form of "singular feminine".
3. regarding the verse 34 of Surah Nisa', I'd like you to visit the answer I posted for this question a few days ago.
4.Concerning the verse 4 of Surah Al-Nisa', there are a few points I'd like to raise so that the meaning of the verse becomes clear:
The verse is talking about the wives who are abdicating their responsibilities. The word "نشز" is originally defined as a high raised land. An arrogant pride and rebellious wife who is shirking her obligations is called "ناشزه" because she believes to be in such an exalted position that she does not have to be accountable to anyone for anything at all.
Getting married involves making a serious commitment. The verse is explaining the ways through which husbands should get the wives to carry out their duties in case they fail to honor their commitments.
This is worth mentioning that the instructions given in the verse are applicable only if the wife fails in the obligations imposed by All-wise Lawmaker. For instance a husband has no right of compelling his wife to carry out the household chores. She is even entitled of demanding money of her husband for housekeeping and even parenting her own children.
The verse is giving a step-by-step instruction on how to sort out such problems. Husbands should be careful not to overstep the bounds when following these steps:
step 1: advising. It is undeniable that when it comes to wives and husbands whose relationship is dominated by love and passion, the way of advising is far cry from the way in which a piece of advice is given to strangers.
step 2: turning his back on her in the bed.
step 3: punishing physically. This approach should only be taken as the last resort to get a rebellious wife to fulfill her duties and prevent her from trampling further rights in the family. The physical punishment has to be inflicted in such a way that cause no breakage, wounds or bruises at all. Taking the second step while knowing that the firs one will do the job, is considered a sin let along overstepping these boundaries by causing wounds or bruises. That's why in some traditions the infallible Imam tells us to hit her by a brush stick as a physical punishment which means that if someone succeeded in getting her wife to accept her responsibilities through the lightest punishment, he would not be allowed to go any further.
Question: What if a husband abdicates his responsibilities? How can he be held accountable?
Answer: Islamic ruler is the one responsible for getting a rebellious husband to fulfill his duties within the family which sometimes involves punishing him physically.