It sad but I think that the tradicional XC fast steel MTB bicycle is dead. Custom or nothing as Mikey have said.
Now you have many options with 29, fat, plus, enduro, bike packing etc, but the traditional XC, no. Chris Chance still do it, but custom. Independet Fabrication do it but custom. Oxia do it and it is custom but it will be more than 1500 euros with options.
I´m building a Fuji shout light 1995 frame and I love it. I want one like that but modern geometry and 27.5, full bicycle around 9-9.5kg and this is not rare, a Marin Team Issue 1996 weights 10.7kg with a Mach 5 and stock XT components, 520 pedals. This will go with tune, SID, a 1,4kg or less wheel set, XTR etc.
For carbon I have one Dual susp quite fast and weigh is around 11.5-12kg (last time 11,7kg) with dropper post (Divine SL) and a minion DH front tire that weights a lot but grips like no all-mountain tire do.