Depends on the person. I dont necessarily agree. I believe Downtown Disney absolutely brings in the magic and offers far more than any of the "budget" hotels. More food options, more things to do, all right with in an area that many of those hotel guests can walk to.
We don't stay onsite much anymore ourselves, so I'm not super into the onsite hotels, but for a first timer I think it should at least be heavily considered. That's all.