Side note: I lost my last 50pt game with MK and Jarl as warlock, my list also included Bushwhackers, War Wagon, Sons of Bragg. Lost to a Ret, Ossyan, triple-warjack (Hypnos, Banshee, Daemon), Stormfall Archers, Arcanists, 2x Destor Thanes, Dawnguard Sentinels.
My list was for fun/playtesting, but I always play to win!
Jarl does little to nothing for MK, especially since Feat doesn't block LOS

.
Jarl's spells aren't superb for MK either, sad that Tactical Superiority can't be used for that extra slight retreat/re-entrenchment.
I believe I made it a competitive game, but the lack of distinct synergies made for a steep uphill battle!
I cannot recommend MK for Jarl.
ps. With Ossyan, Hypnos' 'no Forcing warbeast' gun is overpowered against Gargantuans which rely on power attacks for their main bread and butter attacks.