I think that after Marty and Spencer both left, the Airplane needed to change. They were really forced to, given that those two members, who both brought a lot to the band, were gone. Had Airplane gone on doing exactly what they were doing before, we probably would be sitting around criticizing them for that. In changing their sound, they did what was definitely riskier, and from some perspectives easier.
I think that John Creach was a fantastic musician, and I agree, what he did with Hot Tuna was very cool. In terms of Airplane though, it's hard to say. Long John Silver is often my second-favorite Airplane album, so I'm not one to put down their later stuff, but it was just very different from what they did earlier. A very acquired taste, most definitely. He does seem out of place sometimes, but a lot can be said for his musical ability, which is pretty much mindblowing.
Trouble in mind, lord I'm blue
But I won't be blue always
The sun's gonna shine in my door,
Shine in my back door someday