When I started reading this, there was yet no harem tag.
I continued because the MC was opposed, and firm about keeping it that way. Which was and is still rare for an isekai with at least or more than 2/3 of the protagonists which are girls.
On top, it had good political intrigues and urban / kingdom development without being too OP.
And about the queen having to be a breeding machine, well no. the protagonist is still OP, he literally took objects from his world on top of having some of the knowledge. The kingdom wouldn't need too much babies on the short run.
Just because a series doesn't have a Harem tag doesn't mean it wouldn't become one in the future, since the tag is being placed by those who manage this site, based on the plot so far in the story. I have seen the Harem tag for this Series on many site before they even introduced the plot of it in the Manga, because they tagged it based on the Light Novel.
Also, if you focus on the plot, it had been pretty clear since start that it would go Harem route whether the Author showcased MC agreeing or not, and it does.
MC being against the notion isn't that different from all those countless Harem series where MC doesn't want to engage in relationship with Women
(even-though they women want to) until the very end, or MC is an Airhead when it comes to feelings so he ignores it all.
Just to inform, the Manga started in 2017 in Japan, but it was already clarified in LN Vol.6
(released in 2014 in Japan), that Freya is getting married to MC
(in Manga that would be Chapter 35-36), and she only needed permission from her family to finalize it.
As for the political aspect, most of it isn't that big, as they revolve around the Queen and the power she holds. But the key one is always about MC and expansion of his bloodline.
For urban/kingdom development, other than the few initial ones like the fixing design issue of Water Wheel
(they already had the tech in that world, but it had design flaws), or working on Glass development
(because it gives advantage in many sectors), or the accounting aspect, there haven't been anything else major yet unlike other series with similar plot style.
And most of the minor development had been focused around the food and maybe some random stuff like the introduction of 4-hole flat buttons, majority of which are all restricted to the Palace for now.
The upgrade of the message sending system in the Twin Kingdom, wasn't really a case of development, but rather a way to sell the tech to avoid problem
(it is again restricted tech for the rich and powerful).
And what knowledge got to do with the babies issues?
Knowledge doesn't solve everything if there isn't a proper answer to the problem.
The current problem for Queen Aura is that, her Royal family doesn't have sufficient members, which forces her to either consolidate all power to herself
(which is a problem itself as other outcry of her being a tyrant), or give key positions to non-family members which could give rise to future political instability.
There is also the fact that, her Kingdom is originally a patriarchal.
The only reason she is able to rule her Kingdom is because she is the only surviving Royal.
Getting non-family members in power position is going to cost her dearly
(which is why she was trying to avoid marrying the other two potential before MC), if her own side isn't strong, and the only solution to that is have having more members by giving birth and increasing the size of the Royal family by creating Branch Families.
As for a Royal family to work properly, they not only need to maintain a Main Family with enough members, but also several Branch Families to directly help the Royal, without taking in help from some external source, which could weaken the position of the current Royal members.
So, you shouldn't be fixed on the notion that they don't need to increase their families size just because they have earth knowledge (which incidentally haven't been used much), when the series clearly presents that it is really important and big issue, that needs to be rectified for both short and long run.