It is a very well made mod. First one I downloaded. I think that a new boss would be good, one that does melee sounds fine. Maybe can't heal but it has a crap load of health. No ranged. Patriach strength melee because any stronger and you'd just get one shotted (nice word hey?)
On the other hand, adding a new boss could be difficult to figure out every attack it could use, how fast it is, what perks are good against it or what style of play helps to beat it. It would be better to suggest a distinct idea rather than just ask for a new boss.
Personally I'd say remove the cloak, remove the heal, make it have more HP than the Patriarch, as well as more resistances agaisnt a variety of things; While keeping its good old 'headshots, arm damage and shield resistances'
The Brute moves faster the more you hit it, I'd like to see this stay, as well.
I'd say remove the '-15% speed when on fire', though. If anything I'd like to see the Brute be hurt more with fire, since Firebug seems to be completely less-played compared to every other class.
When the Patriarch runs to heal, so does everyone else. So I propose that it doesn't ever run away, but keeps the pressure on constantly.
I'd also like, were this implemented, for the Brute to be weaker against things the Pat is stronger against.
As such, Patriarch doesn't like explosives. Make explosives more weaker against the Brute.
The Pat doesn't really care for fire; So make the Brute not like fire.
Etc.
Have the spawn rate 50%, so that no one knows which will spawn; And just before the boss spawns, everyone will change their perks on an guess as to what will spawn.
"I hope the Brute spawns, I'll choose Firebug."
*Pat spawns*
"Oh buggeree."
<Lucky I chose Demo lad>