For the new, untried rider wanting to try proper offroad stuff (not towpaths), modern bikes will on the whole be easier to get to grips with riding than an older one.
It took me a year or so before I was comfortable enough with my technique to venture onto more extreme terrain. Modern brakes and suspension make that transition easier.
Those of us who appreciate the buzz of, shall we say, "less predictable" handling, will always enjoy our old bikes, and may even find our old routes more "boring" on a modern bike as lines and brake-pump fatigue are less of an issue.
There is truth in both claims - which is why it is pretty pointless arguing the toss.