Products, whether it be a tractor or some other major item, all go through improvements over the years. If every time an improvement was made, the OEM was required to reach back and improve all the earlier machines, tractors would be prohibitively expensive. A warranty is an agreement, and all the tractor warranties of which I am aware have an hour usage and a calendar time limit, whichever comes first. And on compact tractors, 99.5% of the time the years expire way, way before the hours are anywhere near the limit.
I'd have thought when the muffler failed it would make a lot of noise and you could have noticed that and stopped mowing. Then a little welding job could have been done perhaps and you would have been good to go without the headlight issue.
Unless items are significant or safety related, flaws in tractors that are covered under warranty generally are "fix as fail". And if it does not fail in the time period, it is not fixed. I don't always agree with this, I think there are issues for which the OEM should be more proactive. But if that muffler handled 12-13 years of usage before failing, I'd say it wasn't a grossly flawed muffler system requiring a OEM to retroactively fix.
I think you are being too harsh on Massey. What you are encountering is normal procedure for all brands. After more than a decade, you asked for warranty. That was pretty bold. They said no, and I'd just fix it and enjoy your little tractor. Maybe in another 12-13 years it will have another issue...and that ain't bad!
Buy the headlight new and replace it, but consider repairing the muffler. 15 minutes with a mig welder will weld a muffler back together and another 15 minutes to add a brace perhaps. $50 ought to fix it unless it is a rusty mess.