I wouldn't have thought you would have damaged the final drive.
Do the pegs still vibe as bad if you are in neutral and run the same revs? What about the rear wheel bearings are they okay?
Actually you have raised a really good point. I put a new rear tyre on last week. Reset the chain adjusters with the axle bolt only done up hand tight, made sure the wheel was straight and had the right amount of slack in the chain, blah blah ( did it right)
And then after torquing the rear axle nut up I rechecked the chain and found it to be as tight as a banjo string.
This is quite common as the rear axle acts as a stressed member to add rigidity to the swinging arm. My last bike was like this too. What it really shows is how important it is to check the chain slack after adjustment. Not only at one point but around the whole rotation of the chain before and after tightening up the axle bolt.
Sorry, I know it's a bit after the fact and it not aimed at you but maybe it will help someone else when they are doing their chain for the first time on this bike
Pull my finger