Quoted from TheShameGovernor:There was a definite style change from Early 70's Morison to Late 70's Morison. Early Morison was good, but simple. Illustrations were clean and dynamic, but color palettes and figure detail wasn't as cohesive as it could be. I think he was just getting a feel for the medium and what worked vs what didn't. I'd call his early backglasses more akin to comic "panels" - gets the job done, but nothing crazy.
I mostly agree with you but a more thorough search will reveal glimpses of that more detailed style before that last 'simple' glass. you posted, the Team One. I really think is also has to do with the subject matter. Abra is trippy and a glimpse of that later stuff, but also something like Big Hit-which is later, still has a somewhat realistic look. I don't think you can make a blanket statement like later stuff always being more trippy/complex. vs. earlier work being more simplistic. IMO