I think the difference is that whilst Batman '89 touches on his origin, Batman Begins is an 'origin movie'. So of course it spends far more time on the origin, and his character development along the way; we watch his journey. With Batman '89 we see him at his destination, then later get a (very) brief look at where he started. I'd say Batman Forever focuses more on Batman's origin that Batman '89 does.
I think you're spot on. They're very different films with very different goals. I see B89 as a way of re-defining the Batman in the consciousness of the 1980s
general audience whose previous impression of Batman was the campy 1960s show.
The goal wasn't so much to show you how Batman came to be, it was to say "this is what Batman is". Basically, by the time Burton came on board, they wanted to hit the ground running from a narrative pov, and leave behind the long origin in earlier drafts over the decade .
Batman Begins was made in a very different context with a very different goal. So Begins is the better origin film by far.
That said, the most
fun I've had at a Batman film in terms of the audience reaction and vibe in the theater, was Batman in 1989.
It's one of those moments in time that you had to have been there to appreciate it, and you can't really get a sense of what it was like by reading about it ,or watching youtube videos about it.
You had to have been there in the 1980s and seen the film and experience the hype to understand why the film was so popular despite its flaws.
The Dark Knight in 2008 is a close second in terms of enjoyment at a theater and the hype around it.
I had a good time watching Begins ,but it was nothing compared to 89 in terms of that electricity in the theater.