Hmmmmm.... Well, learn to live with it had already been my conclusion, but not until I'd established it was indeed an Enfield foible, and not a thing I could fix. Naturally one wants to know the WHY of these things.
But there's no doubting the chain is a bit to slack on this current bike, and I'll see how mine is when it's back from 1st service, tomorrow I hope. The snatchiness was first noticed on my own bike, though slight, but way more so on the loan bike, which does have the slack chain. I'll have a go at tightening it today and note the difference if any.
With regard to torque response, it's fine, very satisfying, to this newbie at any rate.
I've not been aware of any surging at low speed on either bike. It's just that the transmission take-up from no throttle to low throttle is a jump rather than a progression, if that makes sense.