Everyone is entitled to an opinion - it would not be a forum otherwise. And everyone reading this thread can form their own opinion based on the factual evidence presented both ways.
There are numerous examples of blades with rows of Turkish ribbon in this forum, on the internet, in museums and published in books. They are far too many to even attempt to list here. Then there are also numerous early Ottoman pattern welded barrels on firearms.
Interestingly enough, pattern welded blades also exist in Balkan folklore as for example "сабя диплянка" (sabya diplyanka), which in Bulgarian means "saber with folds" or "ribbon saber". This is different from сабя дамаскиня (sabya damaskinya), or Damascus sword, which would refer to one made of wootz. I believe there is a song about Krali Marko, a popular hero throughout the Balkans, and his fight with Musa Kesedzija, in which Marko shatters Musa's damaskinya with his diplyanka.
Here is an excerpt from a Bulgarian folk song about St. George fighting a "ламя" (lamya), which is a 3-headed Hydra like creature, which references pattern welded sabers twice:
че си зема сабя диплянка, (and he took his diplyanka)
сабя диплянка с дванайсет дипли (saber with twelve ribbons)
Разсърди се свети Георги, (St. George got angry)
че си извади сабя диплянка, (he pulled out his diplyanka saber)
че й пресече дор три глави, (and cut off all her three heads)
It is fairly obvious that the song is referencing a blade with rows of Turkish ribbon, especially in the part that goes into details such as the number of layers, in this case 12. The presence of such blades into folk songs would suggest that they were valued and predate the late 19th century.
GP's question on blade form is a good one. The examples with a widening toward the tip look similar to the machairas and falcattas of antiquity, and probably handle similarly. I am not a practitioner of HEMA, Kali or any other martial arts, so maybe someone with such a background can comment more on this.
An alternative explanation may have to do with these earlier yataghans being derived from Balkan utility knives, such as the shepherds' knives in Bulgaria, which are shorter and wider compared to the longer and more elegant blades into which yataghans ultimately evolved.
Here are some more examples. The first one is from the Bavarian Army Museum in Ingolstadt. It is interesting to see the rings on the scabbard for a baldric:
Then there is one published in the recent Gold and Damascus catalogue, # 75, with a long 80 cm blade and nine layers of twistcore:
