Yeah, well, that's all water under the bridge, toothpaste out of the tube, and whatever other metaphor you want to come up with. Point is, Jabba is in TPM. So if you were to watch the saga in a linear fashion, the point of building up the character for a grand ROTJ appearance is moot. Otherwise, as I said about the rest of the criticisms, "All true."

Jabba is in TPM for less than a minute, then he isn't back until ANH, then he's mentioned in ESB, then makes his final appearance of course in the first act of ROTJ.
A supporting character whose appearances are spread out like that over a 6-part story isn't that big of a deal. As far as "buildup," what the Jabba / Han scene in ANH does for me is lessen the tension of Han's line "...but we're a little rushed, so if you'll just get on board we'll get outta here..." Or maybe it doesn't. I haven't watched any of the Star Wars movies in at least 2 years or more, so I plan on watching them in number order (Ep.1 - 6) when I get the Blu-Ray set, and just see how it works.