To Mathias' note I would suggest that Richard Sachs, Mark Nobillette and Joe Starck were the most notable early builders.. along with but ahead of Waterford. But I suggest that mostly because doing so illustrates a point: that there's a lot of subjective measure as to what or whos is "better."
As the others note, Grant has always been very adamant that all of Rivendell's "factories" are equally good, so who are we to challenge that. As the others state, having Toyo make larger batches was just one step in a continuous and ongoing process of trying to keep the bikes affordable.
All that said, and since I own a couple of Toyo-built models, I like to IMAGINE that they have some special magic. If you can find the Reader article, it is pretty interesting. I want to say mid 40s in issue no. The biggest thing, if I remember correctly, was the amount of experience and expertise the builders had. There were several "tiers" of craftsmen, with the most important work being left to the seniors. (Or do zI have this mixed up with Nitto??! Maybe both?) They were/are true craftsmen, seeing brazing as a calling and lifetime career, and multi-generational in some cases. In theory, experience keeps someone from over-heating a tube, or impropperly filling a joint, and "could" make a stronger and prettier frame. In practice, it probably doesn't make much difference. I don’t know if there's room or appreciation for that level of craftsmanship in the world anymore. I bought the Japanese Steel coffee table book from Riv. It is nice to think about a time when that culture DID exist.
There were other, minordetails that only an overly obsessed bike geek would care about, like: subtlely s-shaped chainstays on the Atlantis; graceful, double-taper seat stays on the Rambouillet; and artfully thinned edges on the lugs of the Saluki. Many of the high-quality steel tubes that era are no longer made, but I don't know if they were superior or not. Tubing manufacture and metalurgy is a huge rabbit hole to jump into, if someone was interested. Grant has always shunned the ultra-lite, exotic tubes in favor of durability, anyway. One other interesting thought is that, in that era, the frames were 100% brazed (maybe with the exception of canti posts). So a damaged tube or stay could theoretically be replaced with greater ease.
All the design refinements manifested in the newer models certainly out-weigh any artisan touches of the old models. Some day, when China takes Taiwan, we're all going to wax nostalgic about what we have now!