I am still riding what I know from Bitd, so what is modern, I have no experience and so just ride within my capabilities as I have always done.
But an observation perhaps, but retrobikes seem to me to be more road specific design as though well they were really beefed up road bikes that could do a bit of off road, whereas what I am seeing now, seem to be designed for pure off road. As it is in my locale, on the road, my mtb has far better manners than what am noticing of modern bikes which appear to be downhill specific designed. So what I am understanding is the retro MTB's are a compromise between everything whereas what is now is not so much of a compromise.
In fact my one and only bike, the '95 steel GT looks fragile compared to the modern stuff, but it also looks a lot lighter and with richer colour than what is now.