I'll add U.S. 180 to this discussion. With regard to 62, it was established across Texas and New Mexico more than 10 years before 180. I think all three of these routes have "issues" with their routing. U.S. 180 is a logical route from Ft. Worth west to El Paso, providing an alternative route that is well separated from I-20 and I-10 and serving population centers not served by those interstates. The extension in 1962 along what was originally U.S. 260 from Deming NM northwest to Holbrook AZ - and its further extension to the Grand Canyon - really didn't make sense because there is no true relationship between those two segments. I'd really rather see that original designation return, though Arizona has a major state route now with that number. As noted previously, 62 steps south and west from Oklahoma rather than having a straighter alignment. Thus, between 62 and 180, the latter is the more logical designation where they are concurrent, regardless of the novelty of an El Paso to Niagara Falls route.
Then there's 85, which isn't marked for about 600 miles between Fountain CO and the NM-TX state line along I-25 and I-10. New Mexico doesn't acknowledge its existence and Colorado only uses it for local routes still in the state system along I-25. U.S. 85 isn't even continuous in Colorado, and the state marks the Walsenburg business loop, which is technically U.S. 85, as I-25 BL instead. (I haven't forgotten the equally invisible 87, it's just a different topic). There is no need for an additional designation along I-25 south of Denver that I can see.
Given that there is a "wasted" U.S. x5 route here, I've looked at alternative routings that would at least extend the route over its own unique routing rather than having it concurrent with an interstate over most of its southern extent. One was already described above, replacing U.S. 285 with 85. Another idea I've had is to use it on routes designated for future improvement, namely the Heartland Expressway and Ports to Plains Highway. You could route U.S. 85 over SD/NE/CO-71 (the Heartland) from Rapid City south to Limon, then pick up U.S. 287 to Amarillo. From there, I haven't worked out in detail what the routing could be across Texas to the Gulf, and I don't want to replace or create a long concurrency with U.S. 83.
Unfortunately for this idea, Colorado has done squat with its Heartland Expressway portion. CO-71 is a terrible road south of I-76, narrow with pavement in very poor condition. AASHTO would certainly not entertain this idea without a plan to upgrade the road. And, I really don't see the traffic demand for a major route in this area.