Trails in the whites can be hardened and there have been attempts in the past and ongoing to do so on major trails that have been allowed to degrade. Old Bridal Path was maintained for year by volunteers but the volunteers dried up and a lot of their good work got bypassed by the public. When I hiked in NZ the government funded trail building and maintenance, on one popular trail, the Routeburn Track very similar to Crawford path, their budget 10 years ago was $300,000 per mile for maintenance. They flew up one yard bags of crushed rock with a helicopter to level out the trail and keep it dry.
If you look at the start of the rebuild of Old Bridal Path, it looks like the AMC is effectively going to build a very hardened trail. I expect a similar effort will be put in place on Falling Waters trail and expect the section along the brook and the falls may end up looking far different in the future as long as the money lasts and AMC gets their cut for managing it. I think previously I commented on the work done to date as "too good" Rather thana rough trail, they are going with rockwork that most people would love as their front steps. Great if resources were unlimited but they are not and IMHO, it would be best to spread the money around. Somewhat similar to the Crawford Path work where the local rocks were not good enough so they hauled in more via helicopter.
It predates me but people tell me that the lower section of Tuckerman Ravine trail used to go directly up the slope instead of the long stone lined switchbacks suitable for snow cats was built. I was in the area when the FS shut down the stretch between Hojo's and the upper Ravine for at least a season to completely rebuild and harden the trail. Lots of very large boulders were moved to create a rough but hardened set of steps. AMC reportedly spent a lot of resources long ago in building the Twinway from Greenleaf up to South Twin, that long ribbon of rock is not natural, it was built. RMC has been doing major trail reconstruction on the Northern Presidental's since they have had a paid crew and before. Look at trails like Lowes Path and they are nearly solid rock work. Lowes is now hardened to the point where micropikes are not going to do much but get dull on the rocks. If they can get the funding they have the skills but with the number of trails they have, they will never finish.
One of the claims to fame of the Grafton Loop Trail was that it was built to modern trail making standards, the work up the south side of Mt Speck is lesson in switchbacks and drainage. I dont now how many except to say numerous. The tradeoff is the slope never gets steep and the drainage never gets up enough velocity to erode the trail as its directed off. If I remember correctly it took joint crews from the state, AMC and MATC several seasons to complete the trail. MATC spent 17 years rebuilding the AT down off of Whitecap in the 100-mile wilderness and have spent over a decade with a full time crew in the Barren Chairback range. It can be done but it would require a very large block of specific funding. I know the RMC just barely scrapes along keeping a summer trail crew having volunteer work trips to collect volunteer hours that they can use to cover their share of funding agreements plus they ask the club members to donate to support the crew.
On my fall hike on the PCT in Washington State, the terrain was different but just as rugged. We happened to hike over the Kendall Katwalk that is represented as the most expensive mile to build in the PCT.
Kendall Katwalk Effectively they just blasted a footpath in the sides of steep granite slopes. You can see the drill marks in the rocks and in some places they have steel pins drilled in the side of the trail to keep rocks from sliding off, in few spots the trail gets skinny where rocks did slip (with a 1000 foot fall below. Throw in some nasty weather and wind noise and they could have filmed the Fellowship of the Ring party heading up to the gates of Moriah along this section. We hiked 73 miles and every bit of it was 3' to 4' wide well graded climb or descent from one valley to another, switchbacks galore, rarely if ever did we have to break pace due to the steepness of slope and we never needed our hands to climb a slope. In some cases, we were effectively on a one 3 to 5 mile uphill slope to gain 2000 feet with a similar hike downslope. The difference with the PCT was that when the national trails act was signed in 1968, the PCT was mostly not built and the majority of it was built by federally paid for labor (NPS and USFS). They also used horses to build it as the trail was built for horse travel. This is not lowland stuff, the trail is traversing the ridge line between pinnacles. Most of the budget for the trails act went to buy land out east for the AT while the PCT was mostly already on federal land so it went towards building the trail.