For demons the non-dlc 1-4 hits of medium damage skills are slightly more powerful,on single targets,on average than the single severe damage spells. For Flynn the multi-hit ones are noticeably better since the bonus damage from upgrades are per hit. If there's a group of 4 demons on screen and 2 repel wind and 1 is weak to it though , you'll wish you had the Severe skill , so there's pros and cons.
For the DLC skills:
Refrigerate is waaay better though especially for Flynn. Plasma Discharge is on average weaker for demons than the 1-4 hit medium moves, but its stronger for Flynn due to the extra damage for upgrades being per hit.
There's no Single Target Severe Damage for Electric and Ice.
There's no 1-4 hit medium damage attack for Electricity.
Thunder Reign does more damage than the Single Target Heavies but less than the Single Target Severes but hits all enemies.
Cold World is a hit all ice move with a chance of Instant Death , in terms of raw damage its between Mabufula and Mabufudyne.
Thanks for your explanation.