The term "baidarka" is certainly as broad as the term "kayak" but since the term "baidarka" has only recently come into modern use through popularization by George Dyson's book, "Baidarka" most people will rightly or wrongly understand this as a narrower reference to the Aleut style "baidarka" "kayak" the proper name which is "iqyax"

This is the sole design referenced by Dyson and the design which has received all the attention for historical accounts of unusual speed and seaworthiness. This is the design which has been taken up and built by skin on frame enthusiasts and by myself.

The word "iqyax" just means "kayak" in the Aleut dialect. It is not a different kind of kayak from other Aleut single kayaks. All single Aleut kayaks are iqyaxs. Iqyax is just another way of referring to exactly the same thing as a single baidarka. Arguably it is a more proper term, but it isn't a different type of vessel.

Single kayaks or "baidarkas" from Unalaska, Kodiak, Atka and Akun islands and through out the Aleut range would all be properly referred to as iqyax despite the significant differences in form. It would be silly to assume they all perform the same.

No other kayak surfs as well as the iqyax.

I would be interested in knowing your definition of surfing well. This kind of categorical statement should come with a little evidence to back it up.

Here's a quote about a tandem iqyax "skin on frame" raced in the 1997 Blackburn Challenge during a gale, By author Dan Boyne, in WoodenBoat #143 page 57

A multi hole iqyax is an "uluxtax"

But now we moved onto the backside of the island, where the wind and (5 foot) waves are now literally behind us. Just as our spirits have been beaten down to an all-time low, the baidarka starts to show some of it's magic. In following seas, virtually side- by-side with our rivals, the race now becomes a surfing contest. Once again we mysteriously regain the lead without exerting any extra effort. Silently we thank the wide, ungainly stern and upper portion of the split bow for doing their jobs. I can still hear voices, but they grow fainter and fainter.

I was at that race that year. There were no 5 foot waves that day, but even if they were fairly big, it does not mean that "wide, ungainly stern" and "upper portion of the split bow" were what made the difference. There are lots of aspects involved in going faster during a race on any given day.

FWIW my Guillemot Fast Double design holds the course record for tandem sea kayaks in the Blackburn Challenge and it won its class multiple times including the roughest Blackburn on record in 2000. But it isn't exactly a traditional kayak design so I guess it doesn't count.