Perhaps the term ‘Specialist’ would be of more use if you’re looking to leave the term ‘Mastery’ behind. Specialist lends itself to a more modern era (i.e. Victorian) as well.
You could use these:
Tactical Specialist
In the imperial army, Soldiers are trained to survive in the most hellish conditions and hold the line against the deadliest enemies of the empire. Soldiers are oriented toward close combat with sword and shield. What they lack in outright damage-dealing, they make up for in endurance and self-sufficiency.
I chose Tactical because it implies a knowledge beyond simply blowing everything to pieces, as the description of the class acknowledges self-sufficiency.
Ordnance Specialist
Sappers are the pyrotechnic engineers of the imperial army, their primary duty: blowing stuff up. Fighting best from a distance, Sappers engage enemies with guns and a wide variety of fire and electrical traps, bombs, and ammunition. Whether the target is hard or soft, Sappers have the right explosive for the job and they deal out massive damage with an insane zeal.
I chose Ordnance because the term Demolition primarily lies in the destruction of structures. Ordnance is all types of weapons and ammunition, which this class has training in; the ability to use any weapon/device to reduce the enemy to a smoldering paste.
Occult Specialist
Once hunted by imperial forces in an effort to control arcane power and knowledge, Occultists wield diverse powers granted to them by the three witch gods and rely heavily on the eldritch creatures they are able to summon. Along with summoning, their arcane repertoire includes blessings, curses, and offensive spells that inflict damage with poison, acid, and chaotic energy. Occultists excel with neither sword nor gun but can use either to augment their offense.
That’s my $0.02.
[Edit]
I’d use these too…
Espionage Specialist - This would of course be your thief/assassin class which is ever-popular.
Warp Specialist - A class which is like the Occultist, but they get their ‘magic’ from exposure, rather than training/tradition, etc.