I talk a bit about the evolution and usage of katana/s here - essentially, yes, they were smithed prior to the 1500s (and even past then), but were definitely not the staple go-to weapon of samurai or footsoldiers in any major conflict. I do also go into small detail on how the katana became the symbol of samurai here, which in essence confirms what you've already said - I would hesitate to call it a ploy however, but rather a cultural shift, because that's what it was. In those two comments I also talk a bit on why swords weren't being used often by samurai - tldr: better weapons such as spears and bows. Yes, the katana was used, however not to the extent that some people tend to think and exaggerate to.

However, I wouldn't jump so far as to say katanas were crap - they were good weapons relative to the context in which they were developed, but it just so happens that there are better weapons that were more suited to their respective eras of warfare.

So, to the comment linked:

I am buying 700 year old blades with history, owned by noble families and I'm going to Tokyo to do this.

Very unlikely - there exist, to my knowledge, no genuine or authentic swords from 700 years ago. What blades exist probably do so in various stages of decay and/or rust, preserved in museums or exhibits rather than being sold to people. However, if the figure of 370 000 (USD?) is true, that person may have access to things that can't be found normally. That being said, swords from the Edo period could (and probably do) exist in some degree of cleanliness.

The blades are highly inferior to Japanese steel (tamahagane).

Unlikely, but not impossible. As far as I'm aware no solid, reliable comparison exists (from that era - primary sources) between European and Japanese steel, or European and Japanese swords. By Portuguese contact, and even after when Perry opened Japan up, the world was using gunpowder - at those times, katanas were not brought up as the prime example of Japanese weaponry. That being said, during the 1600s (and even earlier), the Japanese did have access to European steel, and used it to create 'hybrid' armour - I touch on that slightly here, but off the top of my head armour like this would be the best representation of what I mean by a hybrid armour. You can see how the lamellar plating style of Japanese armour is reserved for protecting the limbs, whereas the chest is covered by a plate of steel to better protect from matchlock bullets.

I will also mention that, more often than not (again, as far as I'm aware) most swords made in the latter stages of the Edo up to modern times are smithed through different materials and techniques to those used during earlier years. This means that a lot of the quality is lost, as the user says - from this, it is obvious that no accurate comparison can be made from modern reconstructions as representations of what would have happened with swords made several centuries ago.

If I had to place a "Golden Age" of Katana smithing, it would have to be during the Edo period when artistic flair was more important than the practicality of swords. This is where katana became the symbol of the samurai and where the characteristics common to your stereotypical katana start to take shape, and where beautiful pieces of work were being made. However, it seems that the user is pinning that Golden Era more towards the Kamakura period (pre Muromachi) - I'd say more subjective of the person rather than a solid answer of which one is correct though, that one is definitely up to interpretation.

I will however say that, having never handled a katana in real life, let alone buying them, I may be wrong in the physical aspect of this. Even more so here than in other areas, specificity is key. If that person in question has invested a significant amount of time and energy into their passion, then they are probably more qualified to speak on the topic than I, or any others, am/are.