I converted my 2010 enduro to 2012 spec rear end (which had a 142 bolt through rear). Wheel security is improved- I’ve never had the rear come loose with the bolt through- but have had the rear wheel fall out when on QR- I strongly suspect because I didn’t do it up properly. You can’t make that mistake with a bolt through.
Stiffness wise, I couldn’t tell the difference. If you lean your bike over at 45 degrees and push hard on the flat side of the crank with your foot to generate some side load, it looks to me like you get a lot of the deflection at the rear from the hub to the rim and the next most from the rim to the tyre. I strongly suspect a stiffer rim and more spokes/higher spoke tension would have a much larger effect than stiffening the already relatively stiff hub interface.
Though I guess the counter argument is, what’s different to the front? I can feel that a 36 mm stanchion fork with a 20 mm bolt through is noticeably stiffer than a 32 mm QR fork. Is it all in the stanchion diameter and increased lower to upper leg bushing area rather than the bolt though axle? There must be results from tests on bolt through/non bolt through forks of the same stanchion diameter- but I’ve never seen any….