It's debatable, really. The films weren't explicitly planned so that act one ends here or there. An act break can come at any change in the story, and I think it's more a matter of the feel of the film than Significant Character Decisions. By this analysis, TPM has the four acts I mentioned. Each ends with a significant dramatic event. Meeting Anakin doesn't feel like an act break. In any case, if act two of ROTJ ends with Luke handing himself over, act three begins with the Rebel fleet. Your point being?

As for Anakin being secondary, I actually liked that about TPM. I've said this before: as the first film of the series, it should have a standalone plot, and it does. Why should Obi-Wan be the lead and Anakin the "focus", when Qui-Gon and Padmé are having more effect on the plot? Sure, they could have done it with Obi and Anakin as leads, but it would have had to be a very different story and wouldn't have necessarily been any better than the film we got. In fact, it would probably have resulted in "an entire movie wasted on his introduction", whereas the film as it stands (in its theatrical version and in the fanedits I've seen) is a space opera similar in broad strokes (if rather lacking in execution) to the original intent of the series. Does it have much to do with the overall plot of the saga? Not much less than ANH had to do with the plot of the OT, comparatively speaking.