Hey,

I stopped playing during 3.0 and so have no clue how they've changed the leveling experience.

Since i managed to leave coruscant at level 33, won't that make most of the other leveling planets useless? And what exactly did they change? What happened with doing 5 levels per planet?

They have level scaling now. If your level is over the level of the content you are doing, your level gets scaled down to the level of the content. You can see if you're being scaled down by looking at your character portrait. If you are, there will be an arrow pointing down near your character level with another number next to it which will be the max level for the area you're in.

For leveling, they revamped the leveling process a while back so now you can level from doing only purple missions. These are your main class story as well as planet story arcs. You can choose to skip any yellow missions if you want. Alternatively, you can do your class story exclusively with occasional Heroics / Flashpoints. This makes leveling a lot quicker and more straightforward.

They readjusted the XP awards back in 4.0 so you only have to do you main class quests to level up. 33 is about right if you did all the Tython/Ord Mantell and Coruscant side-quests.

However, you'll still find something of a challenge on the rest of the leveling worlds, because they put level caps on each of the worlds. When you head to Taris you'll have your stats mostly capped at level 22 for example (Mastery, Endurance and Power get capped, Crit/Acc/Alacrity are not, but you also need more of those stats at higher levels than lower ones to get the same results so it mostly works out).

You do keep any trained abilities you have though, which does make the earlier planets easier thanks to a full rotation and required resource management tools you might not have actually had yet when you were really level 22.

As a result, outside of a few places on the starter world and capitol world you're not going to ever face greyed out opponents no matter what level you are.

The big advantage for me and my alt-itis is that, once I get my ship*, I can actually level up toons of the same class by running completely different stories. On one I might do the class quests, on another just run the planetary story arcs, a third run only the side-quests while a fourth levels up just running all the heroics.

* Technically you don't even NEED the ship since there are Heroics on every major planet except Quesh and the heroics have Quick Travels with a one-hour cool down attached. Just get to level 10 farming mobs on the starter planet, then head to the fleet and pick up a heroic from each planet and you can more or less go wherever you want without even bothering to start the class missions.