Well, I would argue that the attempt to balance in DDO, by following the 3.0/3.5 rules has made multi-class a generally difficult option, especially for casual players and/or players who do not have uber loot. HSinclair said before she left Turbine that she would never multi-class. I think for the vast, non-powergaming universe, that is sound advice. I find "splash" multi-classing the "inexpensive" work-around which could be called into question.
I find it ironic in many ways. DDO seems "afraid" to give power to true multi-class, perhaps due to "inexpensive" prices that might be gained from sharing in different classes. Yet DDO gives the power right back to classes with UMD and unlimited supplies of non-class restricted clickies.
Which is more to the heart of D&D - creating a character that has well-rounded abilities and working at them or giving classes "free" abilities they would not otherwise have from loot such as haste clickies, unlimited healing pots, etc.?
I guess I just have to question the whole "balance" argument given the state of DDO today. If DDO was truer to pnp rules on loot distriubution, perhaps I would find the balance argument better. I would rather see people invest in multi-classing than be given magic items that circumvent having to go without abilities or rely on their party members. And for the soloers, if multi-classing, without the whole "synergy" requirement (and who determines synergy anyway? why can't a fighter and magic user have synergy in a made-up world?) they would be better able and equipped to handle quests as well.