Regarding #8: jack-of-all-trades
One way to let a jack-of-all-trades character shine is to introduce situations that are well suited for them. For example, in a single dungeon:
Have a combat against a Tinkerer with a flying contraption.
Have a combat against a Monk who easily catches any Missiles and Thrown weapons. His now!
Have a combat against a Sorcerer who Counterspells everything.
Have a combat against a Trickster with a personal vendetta against your Bard -- but will happily concentrate murder on another squishy if their current target of choice is unavailable.
However, the problem with flexibility is that it's invisible and feels useless when it's not needed, but shines too brightly when it is.
Without forcing the situation, the jack-of-all-trades is left wondering, "Why am I playing a Druid, when I could instead be playing a Double-Striking Fighter; or a Mad Wizard; or a healing-specialist Cleric?"
When it is forced, other players are left wondering, "Why can the Druid sling Spells at the Tinkerer, body both the Monk and Sorcerer with Polymorph, and keep our Bard alive (with the Cleric) against the Trickster, all at the same time? Our Barbarian and Dwarf might as well have just hurled verbal insults, for all the good they were doing; our Ranger has clearly never held a pointed stick before (and did we ever recover the Hammer our Rogue threw?); our Wizard is still moaning about their self-inflicted wounds; and our Paladin Guarded the wrong people!"
Maybe the solution is to design combats so that Druids can deal consistent, flexible, damage, but players who aren't dealing damage can noticeably assist in some other way.
Maybe the Tinkerer uses up fuel to swerve on every missed attack, and lands sooner to open up Melee again.
Maybe the Monk has fewer attacks based on the number of Missiles caught, as his hands are full.
Maybe the Sorcerer is noticeably discomforted as she rapidly burns through her Spell Slots, and surrenders once she's out.
While damage flexibility is nice, it usually ends up being unnoticeable or too noticeable, and its value drops in repeat runs once the player knows what dangers await them, and therefore how to adjust their builds to counter them.
Cleric main / Druid secondary