I will pile on a bit to add to the history lesson.

You have a valid point in that my old school Yeti , or the OP's ARC i posted a pic of earlier is not that far removed from Happy Feet 's MArin or any number of old hardtails in theory. Simply swapping framesets back then with all other things being identical would not make you 10 seconds a lap faster on your favorite trail --

So why? I dont know -- why is a 1963 Split Window Corvette worth more money than a '72 Mustang notchback? They are both just old cars right?

I raced mountain bikes and motocross concurrently in those days and YEti was one of the first avid and outspoken cross-sports marketers. They knew that MTB's in that era were popular cross training options for motocross athletes and supported several athletes like Johnny O' MAra, - who went on to become a pro mtb racer (XC) after retiring from motocross. O'MAra riding for YEti along with the likes of JEff Stanton and moto journalist Zapata Espinoza running Yeti logos on their helmets made people in the moto community curious about the brand

Jody Weisel, editor of Motocross Action magazine, even had a hand in designing the YEti Ultimate raised chainstay bike. This cycling and moto crowd inter-mingled quite a bit in those days , with Richard Cunningham even being the man behind Mantis bicycles. (not to mention, Horst Leitner, MErt Lawwill, PAul Turner, Jim Felt -- among others)

But where a lot of mountain bikes resembled road bikes with knobbies and flat bars, the YEti's borrowed design cues from old school BMX (looptail chainstays ) and cyclocross bikes (top tube cable routing)

This along with the founders vision of how he wanted mountain bike racing to be. John Parker was an oddball compared to the cycling mainstrem then. When John Tomac was hitting the Nationals for Yeti, PArker made sure he pitted out of a box van , just like the motocross teams did. HE tooled around the pits on his clapped out Indian himself , and he gave a lot of young, unknown talent their first shot.

Juli Furtado had the MTB experience of a cat 5 beginner when she won the world championship race in 1990, but she had a motor and was aboard a Yeti . Would she have achieved success elsewhere? MAybe, -- but Yeti gave the beginner with the big motor a shot. Very similar story with Missy Giove. Cross marketing by giving bikes to PAul Tracy (Indycar guy ) helped plus the early innovative ideas (carbon tubes, bonded aluminum, too many kooky downhill bikes to count , etc etc. ) plus the distinctive team color schemes and their strong ties to the moto community made YEti the bike to have for a lot of people .

Plus limited regional marketing made the bikes hard to get. There was not a dealership east of Colorado

Eventually . PArker sold out - In the very late 90's /early '00s they were swallowed up by the Schwinn wrecking ball (like Trek did to Klein, Bontrager and Fisher ) - but Schwinn had a lot of problems of their own and thus failed to really grow the brand any further . Other brands became the hip, cool and edgy face of mountain biking (Santa Cruz is the first to come to mind, but there were others )

So in answer to "why" regarding Yeti

Exclusivity
hand built and hard to get
grass roots race effort - almost like a guerilla marketing campaign
anti-establishment
pushed design limits for the time
moto community tie ins
stylish (for the time) design cues and colorways
not to mention fostering a FUN aspect to mountain bike racing


But yes - there came a time when geometry settled in to what worked on NORBA style trails and there were many similarities between brands.

Playing devils advocate, id venture a guess that the same imaginary rider , hypothetically , could pull the XT or XTR build kit and wheels off a YEti, (or S Works or Fat Chance, DeKerf or whatever ) and build a generic Supergo or Nashbar cromoly frameset from the period and have almost identical results by the stopwatch