If you like 2d and want to focus on it, learn a dedicated 2d engine or framework (not Unity). Those have features and workflow focused on 2D and less other stuff to get in the way. The performance is also generally better.
But if you want flexibility UE is a great choice. 2D and low end mobile is not its strongest areas, but there are as you know many other advantages.
And as others have said, if you got a long term plan to make a living making games, focus on becoming really good in one area so you can work for company as part of a team.