Contentment is different than being complacent or apathetic. I do think it's unlikely that an ESTP is ever going to feel the same amount of complete satisfaction with things as they are compared to an ISTJ. On the other hand, I don't think anyone must have an inner nagging restless, rolling stone gathers no moss compulsion at all times if they are contented.
I've come to believe that that sense of inner relaxation and peacefulness comes largely from having your need for secure attachment to others addressed. Otherwise, it's like an alarm bell that has been going on for a long time, but the hearer of it was not able to remedy the situation. Therefore, after much time goes by, they cease to register it as a call to action anymore and it just becomes a low level constant anxiety that makes them restless and uncomfortable without knowing why. They then need to seek outside stimulation to quell it temporarily, but whenever they are alone it comes back. They may try to numb those feelings away by substance abuse, food, screen time, porn, music, work or remaining incredibly busy, but it always comes back. An increasing number of people in our society are dealing with this sense of restlessness and lack of contentment. They tend to believe that a change of person or situation in their lives will be the answer and are disappointed when it is not. I believe true contentment involves addressing your basic needs, so that you have the energy left over to care for and interact with those around you. In the process of allowing others to care for your needs, and learning to care for others', a sense of trust and ability to be vulnerable with them develops and attachment roots can go down deeper.
That, however, is separate from what you find satisfying or what kinds of pursuits attract you. Any of the ESTPs I know seem to be happiest when they have 100 things going at once. They are like border collies that start chewing on the table legs if you don't give them something productive to do - smart, but need lots to occupy their time and attention or they become destructive.
In short, I think that it is possible to be ambitious or wanting to stretch yourself as a person, while still being basically contented.