I know it is a 5e thing, but I feel the rule about giving some classes less on multiclass if you multiclass in the "wrong order" to be kind of annoying. As anyone who has played a few games can tell you, if you want to multiclass as a Sorcerer or Wizard, you always choose Sorcerer or Wizard as your second class because that way you don't lose anything. Fighter-then-Wizard has more hp and Heavy Armor Proficiency while Wizard-then-Fighter does not (and gets nothing better to replace it). I don't see what the big deal would be if you just got the best number of Skill Proficiencies (e.g., if you got 2 from one class and 3 from another, you would get 3), all Armor and Weapon Proficiencies, the starting hp of the best of your multiclasses, etc. The only thing I would leave keyed to your first class choice would be saving throws and that's only because fixing it is not trivially easy (I would actually find a way to fix it, but I think that's a little beyond the easily implementable request to just make the order in which you multiclass not result in clearly suboptimal results).
I know you can just respec to change the order of your multiclass, but it seems like an unnecessary step.