Tange Ultimate Ultralight only came out in 92, and was only on the scene for a couple years - I'd guess 92-93.
A bit too light?
Nah - just that steel started it's decline in popularity for high end bikes in about 92. Just bad timing.
Tange Ultimate may have come out in 1992, but few 92 bikes were made of it. The decline of Tange did pre-date the decline of steel generally, but you'd have difficulty detecting either in 1992. Ultimate Superlight was still being used for top-class bikes such as the Voodoo Bizango as late as 1997, and the various levels of Ultimate dominated top-end steel bikes between 1993 and 1995.
Ultralight was a bit of a misnomer. Even Superlight was not a particularly light tubeset, and so-called Ultralight was heavier than Superlight. Although RM used Superlight for the Altitude and Ultralight for the Blizzard and Equipe, the cost to the manufacturer was the same. The premium price for the Altitude just reflected the fact that it was built by senior craftsmen, and of course the 'lighter is better' myth.