If we are OK with mixing arcane and divine spellcasters into a super versatile multiclass that doesnt take a hit in max level spells, why not also let Fighters and Barbarians dip and mix for more fun?
Let them have Battlemaster maneuvers, Action Surge, Rage and increased movement without postponing their Extra Attacks. After all it's much more fun when your character has more abilities. Sprinkle in some Ranger spells too but make sure they still get Extra Attacks at 5 and 11. Just keep adding more fun into multiclassing until the classes don't mean anything except some skill templates.
It's a fairly common argument that Extra Attack should be based on your combined martial level. Cantrips scale with character, not class, level after all. Why should a Rogue 10/Wizard 1 or a Cleric 6/Wizard 5 get a 3d10 damage Firebolt when a Fighter 6/Barbarian 5 can't attack 3x per action?
