This has been here before. I believe you used the wrong cut of meat plus you should never really boil a brisket.
Many markets sell you a bottom round which becomes shoeleather.
Most supermarket delis use already cooked cb s and are bottom round, but are pretreated to be tender .
A brisket is the best cut whether you pickle it or store bought is the best. With the one you have I would make corned beef hash.