I recall once, a long time ago, popping on on the CharOps board to see the best way to build a Shadowdancer. It turns out, the best way is Barbarian1/Fighter1/Rogue3/Guildthief5/Shadowdancer10. That's TOTALLY what I think when I think "shadowdancer", right?
I'd like to see either some strict limit on MC (two/three classes max) to keep dippers from doing so. The pre-req idea is a serviceable substitute.
Well no, but might we suppose that most people wanting to play a Fighter won't be wanting to put weak stats into Strength anyway, for example?
You don't need to regulate people's initial choices of Class, just provide the encouragement of the best use of Ability scores to support the choice. Multi-classing, however, does need some control - I think the prerequisites work pretty well in that respect.
I can imagine a character with 6 Strength and 16 Intelligence starting off in the wrong Class as a Fighter, before realising that his true calling lay in the use of magic. I can't really see the reverse being true however.
The prerrequisite idea is awful, I'm not against it as an optional rule, but as a beseline I hate it. It really only punishes players and enforces cookie cutter bland characters, also such strict prerrequisites greatly detract from one of the biggest strengths of level by level multiclassing and that is organic character growth. I can still remember two of my characters who weren't exactly a good fit score-wise but still made sense to multiclass, a nimble sorcerer with a wis penalty who multiclassed paladin, and a charming rogue with a somewhat low wis (13-14) who mutliclassed cleric, none of them were a by the book memeber for the second class, and in some aspects they were suboptimal, but story wise it made all the sense in the world for them to do that multiclass and they were pretty fun to play. whereas this new system with heavy prerrequisites says "screw them, none should dare enter a new class if aren't already a living stereotype of it"
Besides you don't want dipping, you are out of luck, the system already allows for a character who can easily get six classes, stat dex 13 wis 15, con 13 (very easy given the high point buy and the godly humans) start as rogue (or paladin, or fighter or bard) then feel free to take levels in druid, cleric, ranger, barbarian and monk as you see fit. Heck stat up a human as dex 15 wis 15 Str 15 int 10 con 13 cha 13, start as mage or bard, bingo you get a character that can have 9 out of the ten classes. But no my slightly above average wisdom assassin cannot repent and turn to a life of cleric on an attempt to redeem herself, because she dared to evolve organically instead of rigidly planning such a turn from day one . [Besides I also dislike the mage prerrequisite automatically is assuming a wizard (high int), not a warlock (high cha or con) nor a sorcerer (high cha) nor a psion (who could easilly favor wis along with int)]
So as you can see the current prerrequisites don't work that way, they don't prevent the mad level dipping some are quick to demonize, but instead they are only there to stop people who want to use it with moderation.