Honestly, I don't think it takes squishing the later experience into the sooner (though that would help) so much as universal design improvements.

Imagine, for instance, if the breadth of abilities seen by level 40 or so were the cap. What could make that experience fulfilling?

A lot of it can be small things, such as dynamic animations allowing for our Heavy Shot to actually point at our target, instead of directly in front of us regardless of player position.

Others would likely be pivotal, such as some actual/interesting mob scripting or "AI", or some reason by which timing would matter or positioning would feel applicable even in solo play.