The way I see it every player has to decide why they keep returning to the game.
If you are returning time and again because you feel a need to acquire that New Thing which you don't have yet then you're probably a Collector and there's a high probability that when the game no longer has New Things to give you then you'll lose interest and move onto the next game which can offer you New Things.
If you are a Completionist then you likely feel the need, or obligation even, to grind away at the game until you have collected every tiny thing it has to offer; most completionists that I know immediately move on after they finish collecting every item, character, badge and thingamabob in the game.
The last type is the player who keeps coming back because they have fun, and while they might also be a Collector or a Completionist but if you find the game fun enough you keep coming back even after it runs out of things to give you besides entertainment value.
Garden Warfare 2 is at the point where if you are a long time veteran you need to decide whether or not the game is fun enough to bring you back.
For me the answer is "yes". I have every character already and all but a handful are at Master level and my character wardrobe needs only about 900 more items to be completed but I have enough fun that it won't matter when I run out of levels or items to get- I'll still keep playing.