"Optional" areas and no level scaling make game too easy?

Not really at all. As a long time player of RPGs at the highest difficulty levels and a compulsive completionist, it does barely anything. Almost no one can properly balance a high-level RPG properly, especially in the last 10+ years. All the highest difficulty does is make the early game harder and/or more frustrating and the fights longer. In most RPGs I've played, once you hit the mid-levels about 1/3 to 1/2 way through a game, you have a large enough arsenal of abilities to make nearly everything easy, regardless of difficulty level. The more side content is available, the worse this problem gets and the earlier in the game it starts. Makes it really difficult for games to be, well, difficult to completionist players like myself.

So on topic, yes, optional areas do contribute to making the game too easy. But level scaling doesn't really help all that much. Once you have enough strong abilities, it takes more than that to make things truly difficult (without being grindy/frustrating, a la health sponges).