My protagonist being needed for my story is a life changing event, does that mean the event needs to be in my story?

This might be completely personal preference, but I would definitely start with the whole exploring thing. It's a great way to establish your MC, and can act as a good contrast to the more compelling segment that comes later as things start to get serious. It can give your story a kind of scary shift, making your reader comfortable in the setting of the MC peacefully exploring the planet, with the occasional minor conflict here and there, before suddenly slamming the reader with a looming threat.

The whole shift in treatment, the MC being an unproductive outcast at first and then suddenly becoming essential, that is gold. You want to harvest the goods of that aspect, and to maximize the impact of that shift, you can't just include it as flashbacks. The reader needs to experience this gloomy state of being an outcast, and then experience the thrill of finally being accepted again, as well as the thrill of proving everybody wrong by the MC showing their worth.

Though, this is probably mostly my opinion and not the objectively better way to structure your narrative.

I've read a couple of stories where there are two storylines in roughly alternate chapters, from different time sections of the same narrative - I think 'Holes' by Louis Sachar did this to a certain extent (although it's ages since I read it) - the 'main' story is about a boy dealing with a curse of some kind, while the secondary 'earlier' story is about his grandfather and how he managed to get the curse laid on the family, culminating in the reader figuring out how the curse has to be lifted (shortly before the main character in the later storyline actually manages that).
You want the 'earlier' climax / revealing point to be reached sometime before the 'later' / main one, so that all the later events make sense and slot into place in the reader's head. It's essentially a much less obvious way of setting the scene, I think.

Because it's such a dramatic moment, it feels like a wasted opportunity to leave it entirely "off-camera." But it doesn't necessarily make sense to start your story there if the main action is going to take place after a gap in time.

I'd suggest that you start your story right before the action begins, and then bring in the backstory as needed and as feels natural within the scope of the story. Maybe that will turn into a full flashback, and perhaps it will just be little glimpses.

It might be a good idea to write out the full backstory for yourself, but NOT to try to shoehorn it into the narrative just because you have it. In my experience, when your backstory is really solid, it will find its way into the story without being forced.