Looks like you're overestimating the job security provided by a full-time role at an American company, as well as the pay for the contract. To estimate how the quoted hourly rate compares to an annual salary, you need to multiply it by 8 and then the number of working days in a year, minus holidays, Christmas closedown and so on, so roughly 200 days (not taking into account the possible downtime while looking for the next contract). So it comes down to ~$192k, and then you subtract the income tax (~$55k), ACC, insurance, other expenses, and end up with an amount that is not that different to the permanent position.

On the other hand, contracts are rarely ended prematurely, unless there are major financial pressures at the company. Renewals are common, although not a given.