The Atlas isn't always "supposed" to be a brawler - the Atlas needs to provide combat presence on the field. For better or worse it's a distinctive chassis, and both enemy and friendly players will react to what it does. The Boar's Head is also an odd duck among Atlases, in that it can actually load up a big enough XL to alter its playing style.
So you can really go a few routes with the Boar's Head - you can play him as a traditional Atlas brawler with an unavoidably hot setup like
This One. Or, you can go for broke with the only 100-ton chassis in the game that can break 70kph, and play a
Clean-Up Brawler who uses LRM harassment to bully people during the early and middle game. Alternatively, you can even
Mix It Up a little. These are only sample builds - which ones, if any, you find useful will depend on your playstyle, skill, and Elo range (due to the responses of your team and opponents.)
It does bear mentioning that if you go XL on the Boar's Head, it's going to be a
really tight build - Atlases are already more limited by hardpoints and space than by tonnage, and adding an XL to the mix really limits you to a couple-three general builds. However, if you can get your Boar's Head into position when the enemy doesn't expect it, you can wreak havok while being able to avoid all but the fastest Assaults and Heavies on the counter-attack.
PS: unfortunately the Medium Pulse Laser is simply too hot to fit into a good brawling setup in most cases. The
Coolest Build I Can Think of Offhand would still overheat in 15 seconds of close combat.