The modern mountain bike was designed to be able to ride up the mountain and come flying down. Something you cannot do on a road bike or cyclocross/love child bike.

depends, some modern mtbs are designed to get as fast as possible from a to b cross country and as you spend longer climbing than you can decending, a bike that climbs faster will get you from a to b quicker.

depends, some modern mtbs are designed to get as fast as possible from a to b cross country and as you spend longer climbing than you can decending, a bike that climbs faster will get you from a to b quicker.

Yes, but you can still hammer downhill in a way that would kill a road or cyclocross bike.

‘You’re not real cyclists until you’ve coughed up a lung on Buttertubs’

That takes me back. I remember reaching the top only for two young ladies wearing wetsuits to suddenly appear from nowhere. I thought I was hallucinating from lack of oxygen, but it turned out they were cavers and had just emerged from a sink hole.
I did a bit of off-roading round there on a CX bike in the 80’s – Malham Tarn, Goredale Scar and so on. The point was to get off the beaten track, not set speed records downhill.
And yes, I am an old duffer!