People used the favorite button for a good reason.

The favorite button was used as a way to bookmark models because it was a simple one-click way to instantly add a model to a list you could refer back to. Adding a model to a collection is cumbersome and awkward. A simple one-click "bookmark this model" button, available direct from the feed or on the model's page, without the need to set options like which collection to add it to etc, would address the need that the Favorite button was previously used to fill.