There are couple of assumptions that you have made. They are:
- We do everything as a Job(Here, from that I mean, Activities performed for the sake of living).
- The number of activities that we can do are limited.
In my following answer, I assume that the intelligence of machines that you are talking about are of the level of a average Human being.
Most of the time it is not the case that what a person does is primarily for the bread and butter. As an example, For a musician, the pleasure which he gets from playing music is the main driving force which makes him a musician. That pleasure can be anything from Unfolding a post experience in a form of music piece, to a pattern of notes. Similarly for a Mathematician the driving force is certainty, beauty, pattern of geometry.
If in some distant future, Artificial intelligent machines are capable of playing piece or discover theorems and proofs, then that won't stop Human beings from doing their jobs, as they won't get the pleasure which they get when they express their experience in the form of music.
Second assumption is analogue to saying that "Creativity is limited", but that's not the case, as The number of things and methods that we can create and innovate, is not stored in some kind of constraint reservoir. Whatever we create like, any job is based on present needs , like if we felt that some place is to be secured, we create a job of "Security guard", and on assuming the future would be not be as present, It can be said that our needs are not limited and from that it follows that whatever we can create is not limited.
So, it can be concluded that however advance AI becomes we would not get to the point in which humanity suffers mass mental illness whose cause is the sense of meaninglessness caused by AI.