If an indie author has 3-5 self-pubbed books that are selling well enough to quit the day job, that author has probably cracked the code for reaching a group of readers that will buy more books that he/she writes in the future. This author has a reasonable idea of how much three more books written for the same audience will generate in royalties.
A $150K 3-book deal spread over three years that would have formerly looked wonderful isn’t that impressive for an indie author who is already earning $50K per year with no limitations on how fast he/she can publish new books and no agent to pay. Particularly if such a deal comes wrapped in a Paleolithic publishing contract that is impossible to understand. (Hint from PG: The parts of a contract that are difficult to understand are prime locations to hide nasty terms.)
When should you self-publish?
Short answer: always.
You write the words, you make the money.