I have four boars, 3 Semogues and 1 Omega and they all took some time to really break in.
Like Badger hair, Boar bristles vary in thickness, stiffness, softness etc. etc. Unlike Badgers, Boars can take a number of lathers to really start coming into their own as the lather machines that they are. The above posted "Ambrose Method" helps, but like all good things in life, breaking a boar takes some time. I can imagine how the 1:5 vinegar bath would help. I have had one round of using that method preceded with a shampoo with dish soaps and followed by borax/water bath.
Not always being known for my patience, I found it helpful to simply make trial lathers at night on the theory that there are "X" number of lathers until the brush was broken. Some brushes take longer than others, but if you latehr daily with the brush, you should notice some improvement each week with some real gains coming after the second week, luxury coming after the third week portending the lather nirvana to come.
Good Lather = More product + More Water + More Time lathering