7 clean

Hello.
As for the issue itself, it is indeed complicated. There is the severity of Rabbi Zira and the custom of the women of Israel who were stricter on themselves, and there is also a dimension of actual halakhic regulation. Sometimes it is strictly legal (in the sense of theft) and sometimes it is more severe. It depends on which of the seven days and the four or five days before them. There is no room here to go into all of that. Therefore, here I will only enter into the fundamental discussion within the framework you have set.
I would also like to point out that there are also relevant discussions on the subject, and you can search and read them. For example, here: http://puah.org.il/%D7%97%D7%95%D7%9E%D7%A8%D7%AA-%D7%91%D7%A0%D7%95%D7%AA-%D7%99%D7%A9%D7%A8%D7%90%D7%9C-%D7%91%D7%96%D7%9E%D7%9F-%D7%94%D7%96%D7%94/
Now regarding the context of your remarks.
First, I very much agree with your feeling that people today tend not to engage in personal issues for fear of a slippery slope. The implicit assumption is that a complex answer, such as it is permissible but there is a risk of a slippery slope, is dangerous and therefore they prefer to immediately move on to a discussion of the second order (slippery slopes). I, on the other hand, think that the danger of the simplistic approach is much greater, because people lose faith in the halakha and the poskim and do not believe them even when they tell the truth that the thing is forbidden (for fear that they are prohibiting it only because of the slippery slopes).
Second, there is room to ask about both custom and complete halakhah, whether they are relevant to our day. It is true that there are mechanisms for changing halakhic law even when the reason is null, but this is a relevant question and worth discussing. Ultimately, even if we reach the conclusion that change is necessary, it may not be possible due to considerations of authority, but there are cases in which it is possible. In any case, it is important to discuss its four aspects: 1. Its substance (is change necessary, is there a need for change). 2. Its substance (is there a halakhic possibility of change). 3. The second order (danger of deviations and consequences). 4. The question of authority. And it is no less important to separate the levels of discussion.
Regarding the change in halakhic law, see my words here: https://mikyab.net/%D7%9B%D7%AA%D7%91%D7%99%D7%9D/%D7%9E%D7%90%D7%9E%D7%A8%D7%99%D7%9D/%D7%94%D7%90%D7%9D-%D7%99%D7%A9-%D7%A2%D7%91%D7%95%D7% 93%D7%94-%D7%96%D7%A8%D7%94-%D7%A0%D7%90%D7%95%D7%A8%D7%94-%D7%A2%D7%9 C-%D7%94%D7%99%D7%97%D7%A1-%D7%9C%D7%92%D7%95%D7%99%D7%99%D7%9D-%D7%95/
Third, even when asking about relevance, it is important to note that there is significant weight to realistic change. For example, in your example, the couple’s relationship was also relevant in the past, and therefore in this particular question it is more difficult to permit based on a change in reality. It is not that there was any fundamental change here. So why was it not permitted in the past? It is true that this is not a categorical claim, since even what was prohibited in the past may be permissible for us to permit and discuss. But this is an important consideration. It can of course be argued that the relationship would have included more aspects of affection and discourse, while in the past it was usually mainly building a house in the technical sense, but I am not sure that is really true.
Beyond that, there are quite a few who claim that this forced separation actually improves the relationship, as the distance causes more desire and longing for the permitted times. I don’t know if this is true and if it is true for everyone, but it is a significant argument in my opinion. This is also a consideration that must be taken into account in the question of the need for change.