I feel for you
I own a '17 AT and love to go offroad as much as I can.
In optimising the bike for this kind of riding, weight is always an issue. I try to pack light and get any bling off the bike to make it ride better off road. No doubt training and skills off road can compensate in place of many KG weight loss, but every bit helps.
I cannot deny it, that center stand has crossed my mind the same as it has yours.
Yes, it is nicer to pack my stuff on the bike when it is level. Stuff doesn't roll off my seat.
Yes, it is easy peasy to lube the chain when on the centerstand.
Yes, it makes tyre and wheel work easier both in my garage and on the road.
Yes, it does give me an option when the sidestand is not up to task, sloping roads
Yes, it does make making riding position adjustments (handlebar, levers, etc) easier
And one that is pretty important that has not been mentioned
Yes, it may take 2cm away from ground clearance toward the back of the wheelbase, but there is a far more sensetive part under there that is also about 2cm lower that the bashplate! The prolink suspension linkage.
The centerstand on my AT goes a long way to protecting that part of the bike. I would much rather dent/break my centerstand than crack that linkage out on the trail!
Yes, it is a bulky, weighty monster of a thing that I would love to ditch if it were just for weight saving
Yes, we can find ways to do most of the things above without it.
But it must be kept in mind, it is adding weight in best place possible on the bike. Static and below the footpegs.
I rock and log jump and make good use of the bashplate. I love to ride gnarly rocky trails, sometimes too fast, but I can' help it! I hope this qualifies me as "someone with experience"
No slap or other clanging issues, yet. No regrets or problems with the centerstand. In fact the leading edge of the centerstand on my bike is testimony to the shite the suspension linkage would have had to take if it were not for that bulky, 'usless' thing.
If I were to develop that slap/clang problem you speak of, I would look at the springs holding it up, or take the advice from the other comments and use some velcro straps or cable ties to keep it in place. Simple elegant solution.
So my verdict is:
Far more usefull than the drawbacks.
I would go as far as to say: if push came to shove, despite using it far more, I would ditch the side stand over the centerstand.