I've owned a few different full suspension bikes from the "modern era," i.e post 2015 geometry and 29" wheels. My current line up is a Santa Cruz Blur and a Santa Cruz Hightower(both 2024 models.)

The Blur has been my XC race bike for the past 2 seasons and has a 120mm fork, with 115mm travel in the rear. My perspective on the racing end of it: hardtails are exceedingly rare now, especially in the pro ranks. Just from my personal experience, the debate is now between short travel XC bikes(100mm travel) and the more progressive XC bikes like mine with 120-130mm travel. IMO, the added suspension travel of my bike adds capability to it, yet gives up virtually nothing to the shorter travel bikes or HTs for that matter...so I think the 120mm fork is a no-brainer.

My trail/all-mountain/"baby" enduro bike is my Hightower. Originally it came with a 150mm fork and 145mm rear travel. I changed out the air shaft in the fork to bump the front travel to 160mm. It replaced a dedicated Enduro race bike(2019 Canyon Strive) and definitely can ride terrain that would be impossible to ride on a hardtail...or at least for guys that aren't sponsored Redbull athletes. The trails I ride on this bike are definitely not everyone's cup of tea and probably don't mirror most riders' use cases.

That being said, when I do go to some of the more popular riding areas, I'd say that most people are over-biked IMO. There's one local area that almost all of the trails are easily ridden on my XC bike, yet I always see a bunch of people on 170mm enduro bikes. I don't judge too hard, for all I know it might be there 1 bike and they normally ride harder trails. If not though, they're certainly giving up some pedaling efficiency and adding unnecessary weight.