No, what a silly assumption to make.
You asked about situations where sex matters so I gave a specific answer to that. There's nothing in my answer to imply I think "assume things are the way they are for a reason" is a general rule for life 🤣. I'm afraid that's you reading in something that isn't there.
In fact if you read my answer properly also said "tend". I'm more than happy to re-establish the existing single sex boundaries as a starting point and then think properly, situation by situation, whether any are no longer needed. I"m pretty sure that hairdressers, for example, don't need to be women-only(1), nor the Masons men-only.
Which is exactly what should have been done all along - an honest and open public debate and carefully thought through change (which incidentally is what happened with opening up marriage ).
Instead we had the dishonest sleight of hand where rather than looking at sex specific situations to see if they still made sense, TRAs insisted the meaning of the word Woman itself was changed, and thereby appropriated everything that was Women-only for trans women without going through any open assessment of whether specific situations were single sex rather than single gender. That was clearly a mistake and should be rolled back.
You're also forgetting that due to the Equalities Act, there was already a mechanism to challenge single sex provisions and many had gone, meaning those we still had were mostly (not all, eg Masons) considered to be there for a good reason.
This may surprise you but I actually don't think any single sex provisions are there naturally . I think the women-only rights, opportunities, protections and spaces we have today exist as specific measures to mitigate the disadvantages we as women (original female meaning) face due to male entitlement, male violence and structural and cultural biases against women. l'd be more than happy to move towards a future where these things have gone away, making single sex provisions simply uneeded. I even recognise that in some ways the solution is part of the problem (eg we have separate toilet facilities today because it wasn't acceptable for women to relieve themselves in the open and because some men behave(d) badly towards women in the existing, de facto male facilities. But now that very separation has led to a lot of men fetishing women's toilets, meaning we continue to need to keep them out, and so it goes round).
But any fair change has to start with removing the need for the separation - the risk/disadvantage to women - first.
(1) And even with the hairdressers, women who have to cover their hair for religious reasons still need women-only spaces. You might say "well their religion shouldn't oppress them" and you might be right, but these women still have to live within their family and their wider social context, so unless you are going to solve that as well, by taking away their women-only provisions without adressing the need for them first, all you are really doing in practice is taking the opportunity to participate away from these women. So you see, even what on the surface look like trivial changes can be significant, which is why we need to go back, put the protections back for now and then move forward slowly, honestly and without preconceptions about what is needed and what is not.