All hero stats are currently inflated to a ridiculous degree on PC/Mobile. Magic is probably at about 5 higher than it should be alone. This is reportedly a bug that will be fixed, but not until next version.
Before you even consider traiting Venbarak, you should look at Queen Mab instead. Ven has Magic Link and costs less mana and hits impervious troops, but Mab is overall better otherwise. She also fits well in teams like Soothsayer/Valk/Mab/Rowanne, Valk/Mab/Row/Mercy, Valk/Valk/Mab/Mercy, Sooth/Mab/Valk/Mab (etc.), and these won’t lose any power when hero stats get fixed. If you dont have Mab or Behemoth, though, it may be worth traiting Venbarak up to the “magic link” trait for faster charging.
Personally, I’ve been using Green Slime/Dragon Soul/Shadow Dragon/Soothsayer just for the change of pace (sylvanimora in the last slot is way stronger, but I like soothsayer better for fast explores). I tried a bunch of different variants for valk/AoE explore teams and some non valk teams and they had nearly identical average clear times over ten battles. Sub-90 seconds on average (worldmap to worldmap) is a good mark to aim for with souls teams if you are going for speed clears, or sub 2 minutes if you are going for two casts to cap souls every fight.
The only non-soul-farming team I’ve found that is significantly faster in explores is using a bombot team with huge armor, such as Deep Borer/Bombot/Imperial Jewel(Mechanist)/Blast Cannon where I can fill in one match and clear in two back to back casts (three back to back casts on a bad board), which was over 50% faster than any other variant I’ve used.