Personally I like the balance gained from the system as is. It helps promote Single Classing (which in my opinion needs more incentives still as I am an avid Multiclasser), and it provides a necessary balance point for Multiclassing.
You SHOULD have to ask yourself, do I really want this trade-off to multiclass? The same goes for the XP ruling (though I extend the level difference by +1).
In your 1st example of a 4th level Fighter/Barbarian/Ranger/Paladin:
* First off this isnt even possible without an Alignment change and the loss of either Barbarian or Paladin Class abilities.
* Second off, Ok, so they have +8 to Fortitude. So What? Its the cost they chose for spreading themselves too thin and weak. Why weak? Because they also have a "+0" to Reflex AND Will! Any caster worth their salt knows better than to hurl a Fortitude dependant spell at a "Warrior" type Anyway so this 4th level dude is FUBAR against any Reflex or Will dependant saves.
I think the stystem is balanced fine "as-is" with the BAB/Saves for multiclassing. Its one of the best mechanics in the class system. And that says alot as I a master of housre rules and system re-writes.
You SHOULD have to ask yourself, do I really want this trade-off to multiclass? The same goes for the XP ruling (though I extend the level difference by +1).
In your 1st example of a 4th level Fighter/Barbarian/Ranger/Paladin:
* First off this isnt even possible without an Alignment change and the loss of either Barbarian or Paladin Class abilities.
* Second off, Ok, so they have +8 to Fortitude. So What? Its the cost they chose for spreading themselves too thin and weak. Why weak? Because they also have a "+0" to Reflex AND Will! Any caster worth their salt knows better than to hurl a Fortitude dependant spell at a "Warrior" type Anyway so this 4th level dude is FUBAR against any Reflex or Will dependant saves.
I think the stystem is balanced fine "as-is" with the BAB/Saves for multiclassing. Its one of the best mechanics in the class system. And that says alot as I a master of housre rules and system re-writes.