Let's see, what did I learn about what was going on with my Warden? Oh, that's right, nothing, because my Warden is dead. I saw the funeral at the end of Origins.
Regardless, your premise is built upon one set of circumstances, those that you chose to use for your observation. What you like or dislike about a game is subjective, and so, while you're not wrong in that regard, where your premise is falling flat is in the assumption that everyone saw it the way you did. The biggest "problem" I have with your premise, and I put in quotes because really, when you're speaking about you feel about it, it really doesn't affect me at all, is assuming that I came away feeling the same feels you did over the same things when, as we can see from the opening question of this post, I didn't even have the same experience that you did in that one aspect of the game, and I'm sure, being who I am, that there are other differences as well.
I didn't get any feels from the War Table mission concerning the HoF, because my HoF is dead, and there was no mission, in my canon playthrough. I didn't get Leliana's angst about returning to the HoF, because she knew the HoF was dead. Morrigan knew the HoF was dead, and didn't have a child to show for her time with her. The continuation of the Legacy story line is to be expected, considering the Antagonist in Inquisition was the Antagonist in Legacy. However, if they had not included Hawke, it would have played out much the same, only we'd have less information going in. They were integral to the story only in that they had previous experience with Cory, other than that, nothing they brought to the table was Cory breaking. We got more from the Temple of Mythal than we got from Hawke, hell, we got more from Flemeth than we got from Hawke. Basically, Hawke's cameo was more along the lines of an exposition of the events of Legacy than anything else, and we could have gotten that from Varric w/out Hawke.
So no, I didn't find my enjoyment of DA I in "fanservice", although I do tend to agree that the War Table mission for the HoF was just that, fanservice. It was, after all, included to appease those that cannot let their Warden go, and must instead have BioWare write an end to their story, despite the fact that really, it should be quite over. That's a discussion for another thread though.