I am not an expert on history or tsuba, but I could imagine both thesis were reality. I don`t think there were any real hierarchy of tsuba that everyone had to follow similar to law of the samurai class. If this was the case I am sure we would have tons of writings on this topic about the differant tsuba them selves and the hierarchy system. The fact is, we don´t.
At this point I would like to remind some that the color of the ito wrapping on the tsuka had this kind of a system at court. Now we know about it, because it was written down as a law <- another fact.
Still I think Toryu and the general Idea of this topic has some truth in it as well.
If we assume that the quality of tsuba was a question of money, then it is probably, that higher ranked samurai (who had more money to their dispance) had a finer tsuba (sword, koshirae, Armor, etc.). In this case you could truly identify a rank of a samurai looking at his appearance, including the tsuba. This is a general Idea, so that the tsuba would be just one element of judging the rank of a person you don`t know. It is important not to forget, that samurai trained on a daily basis. Swords and tsuba was something of an every day life. To identify a sword or a tsuba would not have been something special to them. If I compare this with today, I think anyone of us would identify a ferrari when he sees one (or at least see that it is a fancy car) and not mistake it for a volvo.
The remark of Toryu complies with the code of behavior of the samurai. Imagine you are a midle calss samurai who was saving money to buy a Daimyo calss tsuba. I can not imagine that he would wear this tsuba in public or even go to his lord and show of with it. The code of attitude bindet him to wear what ever he likes - according to his rank -, as it could be an insult to a higher rank otherwise. In this case you could also tell the rank by the quality of the tsuba. Yet again this is also a general Idea and not tsuba specific.
So I think, allthough there were no laws about a specific hirarchie of tsuba, you could actually tell the rank of a person by the tsuba (sword or anything alse, which was rank related).