I must admit, I really like what you have at the moment, and I think that would be a good basis for your introduction. I am very impressed by phrases such as "skimmed the surface of experience." Do make sure, however, that you haven't unwittingly plagiarised such phrases. It can be very easy to do! Make sure that all you write is your own work, otherwise you need to show that it is a quote by putting it in quotation marks and indicating your source. My suspicion is that you have found this paragraph somewhere and are using it for your essay, but it is really important that you re-write it in your own words.
You are completely right, however, when you indicate that it needs to be cut down to one sentence. Your thesis at the moment combines lots of different elements, and my first suggestion to you would be to really consider what the main point is that you wish to make. How is his relationship with Samoa relevant to what you want to say? What is it that you wish to communicate about this author? Answering such questions will help you narrow down your thesis statement and make it simpler and more direct. If it is his work that you wish to focus on, you might want to use a thesis statement like this:
In spite of his lack of originality, Stevenson nevertheless manages to create gripping tales of adventure that reflect his own vigorous relationship with life and art.
If you choose a statement like this, however, you will need to prove that his tales are not original but at the same time you will need to look at how he creates "gripping tales" and how they reflect his relationship with life and art. Always with thesis statements, the rule is, "keep it simple, stupid!" Having a simple, elegant thesis statement means that you are able to focus clearly in your essay on proving what you argue. Good luck!