I've recently finished the game darkside with a monk, thief, sorcerer and paladin. I find GM water magic and M air to be too good to pass on. Monk is an ok-ish night, thief is an ok-ish knight with some cool utilities. Paladin was there for the heals in early game and survivability. Once you get inv, and fly, the game becomes easy. After getting shrapmetal, the game is even easier. Dark Magic in MM7 is so much better than light Magic. I find clerics to be useless if going dark. Can always take a druid or paladin instead for the Spirit Magic buffs and Regeneration to keep you from dying.

No reason to reinvent the wheel.
In MM6 Magic was indisputable and the discussion was whether SSSC or SSSS was the strongest.

In MM7 might was rebalanced with gating magic behind promotions and storyline, while might is relatively unlocked from the start. Furthermore, armsmaster became a thing. The discussions for MM7 is about knight knight sorcerer cleric (Light) vs Sorcerer Sorcerer Sorcerer Cleric (Dark). I think SSSC for mm7 is great and SSSS for mm6. You can find my reasoning on last page of link below.
Class discussion: https://www.gog.com/forum/might_and_magic_series/mm7_party_recommendations/page1
For the druid vs sorcerer you're basically trading away GM Water (item enchant, lloyds), making you miss out on the potential +XX armsmaster enchant which boosts your knights: https://www.gog.com/forum/might_and_magic_series/kmcd_top_mightofcenter_party_for_mm7_theory

Since 2017 my understanding changed a little. Note that when discussing "might" then there is no inherently differences between the classes, especially in MM6. The main difference for MM7 is armsmaster, but otherwise a full party of sorcerers is (early game) just as strong on "might" as a full party of knights, max hit points aside. The issue of max hit points is removed with body magics regeneration. Chest armor where recovery time is not eliminated is a detriment, making leather optimal early-midgame. AC can be achieved through accessories.

Recovery time is the reason for the wonky balance (Google: greyface might and magic mehcanics). You want to hit '30' as soon as possible, and that is just harder using swords (90) than daggers (60). Dual daggers can hit 30 with haste & 25 speed stat. This is right out the game after the starter island! Eventually KKSC catch up when you find 2 'speed' swords for your knights' right hands, but until then hitting 30 from 90 is harder. (90 - 7 sword - 7 armsmaster - 25 haste - 5 speed = 46, 50% slower than the daggers in midgame without speed swords).

With either party, I think a large boost early game is finding/buying 'Mage dagger's or 'Duelist sword's and getting them enchanted through fire magic or water magic (Speed/Vampiric)

TL:DR. 1 sorcerer and 1 cleric is a great addition to any party for GM Water (Enchant item, Lloyd), Air (Invis, fly), Body (Regeneration), Spirit (Protection from magic, heroism), and Light OR Dark.