I seem to recall the VIA KT266a - 333 - 400 chipsets quite popular actually. The only problem was actually some versions of the chip itself.
http://www.geek.com/procspec/amd/thoroughbred.htm
"There's two flavors of the Thoroughbred core, the first hot-running and not-very-scalable Thoroughbred A and the cooler and higher-clocking Thoroughbred B. The "B" core is slightly larger due to a new layout designed to improve scalability"
The chipset problems only occurred with K8 release when VIA chipsets did not have a lockable AGP PCI bus I seem to recall.
I was referring to the Slot A Athlon. AMD's 750 chipset was all you really had at launch. VIA rather quickly released the KX133, though. But the number of decent boards was very limited. ASUS would only release theirs in a basically un-named brown box. It was very slow going for a while there.
VIA's early Athlon chipsets weren't all that great. By early, I mean KX133, KT133, and KT133A. The 686B southbridge was bad news. PCI design was awful. There was occasional IDE data corruption and most of a time a SBLive! would not work correctly. George Breese's PCI Latency patch saved the day there tho, for the most part. The bus had like a pathetic maximum bandwidth of 30 MB/s without his patch. I don't remember how bad their AGP design was, but I bet it had tons of issues too considering how god awful it was on MVP3.
Still, Athlon and Athlon XP turned around AMD in a big way. The K6 days were certainly worse.