Let's consolidate where you're at on this issue, so far:

1. Sex with female slaves was permitted
2. The Qur'an places no limit on the number of female slaves ("what your right hands possess") as it does with the limit on wives (i.e. max four)

Regarding:

have been linked to personal blog posts which is a great starting point but not a primary source.

If that includes my blog post:

Rape of Female Prisoners of War and Ahmadiyya Islam

Then while I add commentary, I have of course, cited with screenshots, a book (Seal of the Prophets Volume 2), just as you have. While the author is careful not to use the words rape, if you read between the lines, this contingency is obvious. Granted, the author couches it as a measure of retailiation if Muslim women captured by the enemy are also being raped. Of course, this is the Ahmadiyya tafsir trying to explain away the practice.

Regarding consent, I suggest you read your post and ask yourself if you're not blurring the issue so as to not have to address it.

Ask yourself, why are certain forms of harrassment especially taboo, such as that being highlighted in the recent #MeToo movement? It's because when there's a disparity of power, you cannot have true consent. If you talk to a sociologist, they'll tell you the same thing.

A true and just religion would have said, "you must free her and marry her before you can have relations". That statement is conspicuously absent in the Qur'an.

One of them is the idea of Mukatabat (pg18) which allowed any slave to demand his/ her freedom and the master had to oblige

I personally think this is a cop out. The rules of Mukatabat are not outlined in the Qur'an. How do we know what defines the parameters as reasonable? Are a slave and a master equal persons under the eyes of the law? If not, whose to say the judge isn't likely to favor the master?

If the slave is a slave, they are already performing chores/service to the master. To enter into Mukatabat is to say, "I'm going to work even more to pay you for my freedom". If they're already a slave, how much more are they supposed to work? Now we're getting into exploitation territory.

Do you see how nonsensical this apologetic line of argument becomes?

On a related note, accepting multiple wives and slavery in Islam further skews the power dynamics of Qur'an 4:34. This was highlighted in a very novel way by Ginan Rauf in the Muslimish Freethinkers podcast episode, A Verse from the Qur'an.