Ah Mick... Everyone has their blind spots - the XR500/600 is obviously yours!
They were, and still are, a good thing. But there's a bit of a mythology building up about these old buses, where their shortcomings are overlooked or forgotten...
Let's see:
Desperately in need of real springs in both forks and shock (but particularly the forks);
Weak footpeg mounts;
Weak third gear;
Stators that die in the heat;
Weak drum rear hubs;
Shitty twin carbs (before 1988);
Hard starting;
Lots of weight, most of it too high;
Pegs too wide and too low and drag through ruts that a dirt bike should be able to ride straight through*.
At least the 600's swingarm is not ridiculously short like the 250's is.
Like 500 MX bikes, there's a lot of things to love about the XR600, but they stopped making them for a reason!
*Back when XRs were everywhere, I could ride my 125 enduro bike through 99% of ruts with my pegs 2 or 3" above the top of the rut. Those that were deeper, were usually wide enough that the tips of my pegs would barely touch the side wall of the rut.
Most ruts had been bulldozed out by the hoardes of XRs, with their low, wide engine cradles particularly when the average rider would use up half the suspension travel just by sitting on the thing...